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Versions: 00 01 02 03 04 rfc2156                                        
Network Working                                             S.E. Kille
Group                                                 ISODE Consortium
INTERNET-DRAFT                                             August 1995
                                               Expires:  February 1996
                             File: draft-kille-mixer-rfc1327bis-01.txt





              MIXER (Mime Internet X.400 Enhanced Relay):

                Mapping between X.400 and RFC 822/MIME





Status of this Memo

This document is an Internet Draft.  Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups.  Note that other groups may also distribute
working documents as Internet Drafts.  Internet Drafts are draft
documents valid for a maximum of six months.  Internet Drafts may be
updated, replaced, or obsoleted by other documents at any time.  It is
not appropriate to use Internet Drafts as reference material or to
cite them other than as a ``working draft'' or ``work in progress.''
Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet
Draft.


NOTE: This document (version 2.2) is change-barred relative to version
2.1.  Some obvious formatting errors have been introducted by this
process, and these will not be present in the final version.








Network Working Group                                       S.E. Kille
Internet Draft                                        ISODE Consortium
RFC 1327bis                                                August 1995
Obsoletes: RFCs 987, 1026, 1138, 1148, 1327, 1495
Updates: RFC 822
                                                                        |

             MIXER (Mime Internet X.400 Enhanced Relay):

                Mapping between X.400 and RFC 822/MIME



Status of this Memo:

     This document describes a set of mappings which will  enable
     interworking  between  systems  operating  the  CCITT  X.400
     Recommendations on Message Handling Systems (1984, 1988  and
     1992  versions)  /  ISO  IEC  10021  Message  Oriented  Text
     Interchange Systems (MOTIS) [2,13,15], and systems using the
     RFC  822  mail  protocol  [16] or protocols derived from RFC
     822, supplemented by the  MIME  specifications  [9].   Older
     systems  which  do  not  use  MIME  are still supported. The
     approach aims to maximise the services  offered  across  the
     boundary, whilst not requiring unduly complex mappings.  The
     mappings should not require any changes to end systems. This
     document  is  a  revision  based on the evolving sequence of
     RFCs 987, 1026, 1138, 1148 and 1327 [17,18,20-22], which  it
     obsoletes.   It  incorporates  changes specified in RFC 1495
     [5], which it also obsoletes.

     This document specifies a mapping between  two  families  of
     protocols, which includes both protocol/service mappings and
     use of a  mandatory  global  mappings.   This  specification
     should  be  used  when  this  mapping  is  performed.   This  |
     specification may be modified in the light of implementation
     experience, but no substantial changes are expected.

     This draft document  will be submitted to the RFC editor  as
     a  protocol  specification.   Distribution  of  this memo is
     unlimited.  Please send comments to the author.






Kille                                                         [page 1]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     2          - Service Elements ..............................   16
     2.1        - The Notion of Service Across a Gateway ........   16
     2.2        - RFC 822 .......................................   17
     2.3        - X.400 .........................................   24
     3          - Basic Mappings ................................   35
     3.1        - Notation ......................................   35
     3.2        - ASCII and IA5 .................................   37
     3.3        - Standard Types ................................   37
     3.4        - Encoding ASCII in Printable String ............   40
     3.5        - RFC 1522 ......................................   42
     4          - Addressing and Message IDs ....................   43
     4.1        - A textual representation of MTS.ORAddress .....   44
     4.2        - Global Address Mapping ........................   51
     4.3        - EBNF.822-address <-> MTS.ORAddress ............   54
     4.4        - Repeated Mappings .............................   67
     4.5        - Directory Names ...............................   69
     4.6        - MTS Mappings ..................................   70
     4.7        - IPMS Mappings .................................   75
     5          - Detailed Mappings .............................   81



Kille                                                         [page 2]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     5.1        - RFC 822 -> X.400: Detailed Mappings ...........   81
     5.2        - Return of Contents ............................  101
     5.3        - X.400 -> RFC 822: Detailed Mappings ...........  102
     Appendix A - Mappings Specific to SMTP .....................  139
     6          - Probes ........................................  139
     7          - Long Lines ....................................  139
     8          - SMTP Extensions ...............................  139
     8.1        - SMTP Extension mapping to X.400 ...............  139
     8.2        - X.400 Mapping to SMTP Extensions ..............  140
          Appendix B - Mapping with X.400(1984) .................  141
     Appendix C - RFC 822 Extensions for X.400 access 143........    [
     Appendix D - Object Identifier Assignment 144...............    [
     Appendix E - BNF Summary ...................................  145
     Appendix F - Format of address mapping tables ..............  156
     1          - Global Mapping Information ....................  156
     2          - Mechanisms to register and to distribute
     Mapping Rules ..............................................  156
     3          - Syntax Definitions ............................  157
     4          - Table Lookups .................................  158
     5          - Domain -> O/R Address format ..................  159
     6          - O/R Address -> Domain format ..................  159
     7          - Domain -> O/R Address of Gateway table ........  160
     Appendix G - Conformance ...................................  161
     Appendix H - Change History: RFC 987, 1026, 1138, 1148
     ............................................................  163
     1          - Introduction ..................................  163
     2          - Service Elements ..............................  163
     3          - Basic Mappings ................................  164
     4          - Addressing ....................................  164
     5          - Detailed Mappings .............................  164
     6          - Appendices ....................................  165
     Appendix I - Change History: RFC 1148 to RFC 1327 ..........  166
     1          - General .......................................  166
     2          - Basic Mappings ................................  166
     3          - Addressing ....................................  166
     4          - Detailed Mappings .............................  167
     5          - Appendices ....................................  167
     Appendix J - Change History: RFC 1327 to this Document
     ............................................................  168
     1          - General .......................................  168
     2          - Service Elements ..............................  168
     3          - Basic Mappings ................................  168
     4          - Addressing ....................................  168
     5          - Detailed Mappings .............................  169



Kille                                                         [page 3]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     6          - Appendices ....................................  169














































Kille                                                         [page 4]


                          Table of Contents



     1          - Overview ......................................    6
     1.1        - X.400 .........................................    6
     1.2        - RFC 822 and MIME ..............................    6
     1.3        - The need for conversion .......................    7
     1.4        - General approach ..............................    7
     1.5        - Gatewaying Model ..............................    8
     1.6        - X.400 (1984) ..................................   11
     1.7        - X.400 (1992) ..................................   12
     1.8        - MIME ..........................................   12
     1.9        - Body Parts ....................................   12
     1.10        - Compatibility with previous versions .........   13
     1.11        - Aspects not covered ......13..................    [
     1.12        - Subsetting ...................................   13
     1.13        - .mc | ......14................................    |
     1.14        - .mc ..........................................   14
     1.15        - Document Structure ...........................   14
     1.16        - Acknowledgements .............................   15
     2          - Service Elements ..............................   16
     2.1        - The Notion of Service Across a Gateway ........   16
     2.2        - RFC 822 .......................................   17
     2.3        - X.400 .........................................   24
     3          - Basic Mappings ................................   35
     3.1        - Notation ......................................   35
     3.2        - ASCII and IA5 .................................   37
     3.3        - Standard Types ................................   37
     3.4        - Encoding ASCII in Printable String ............   40
     3.5        - RFC 1522 ......................................   42
     4          - Addressing and Message IDs ....................   43
     4.1        - A textual representation of MTS.ORAddress .....   44
     4.2        - Global Address Mapping ........................   51
     4.3        - EBNF.822-address <-> MTS.ORAddress ............   54
     4.4        - Repeated Mappings .............................   67
     4.5        - Directory Names ...............................   69
     4.6        - MTS Mappings ..................................   70
     4.7        - IPMS Mappings .................................   75
     5          - Detailed Mappings .............................   81



Kille                                                         [page 2]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     5.1        - RFC 822 -> X.400: Detailed Mappings ...........   81
     5.2        - Return of Contents ............................  101
     5.3        - X.400 -> RFC 822: Detailed Mappings ...........  102
     Appendix A - Mappings Specific to SMTP .....................  139
     6          - Probes ........................................  139
     7          - Long Lines ....................................  139
     8          - SMTP Extensions ...............................  139
     8.1        - SMTP Extension mapping to X.400 ...............  139
     8.2        - X.400 Mapping to SMTP Extensions ..............  140
          Appendix B - Mapping with X.400(1984) .................  141
     Appendix C - RFC 822 Extensions for X.400 access 143........    [
     Appendix D - Object Identifier Assignment 144...............    [
     Appendix E - BNF Summary ...................................  145
     Appendix F - Format of address mapping tables ..............  156
     1          - Global Mapping Information ....................  156
     2          - Mechanisms to register and to distribute
     Mapping Rules ..............................................  156
     3          - Syntax Definitions ............................  157
     4          - Table Lookups .................................  158
     5          - Domain -> O/R Address format ..................  159
     6          - O/R Address -> Domain format ..................  159
     7          - Domain -> O/R Address of Gateway table ........  160
     Appendix G - Conformance ...................................  161
     Appendix H - Change History: RFC 987, 1026, 1138, 1148
     ............................................................  163
     1          - Introduction ..................................  163
     2          - Service Elements ..............................  163
     3          - Basic Mappings ................................  164
     4          - Addressing ....................................  164
     5          - Detailed Mappings .............................  164
     6          - Appendices ....................................  165
     Appendix I - Change History: RFC 1148 to RFC 1327 ..........  166
     1          - General .......................................  166
     2          - Basic Mappings ................................  166
     3          - Addressing ....................................  166
     4          - Detailed Mappings .............................  167
     5          - Appendices ....................................  167
     Appendix J - Change History: RFC 1327 to this Document
     ............................................................  168
     1          - General .......................................  168
     2          - Service Elements ..............................  168
     3          - Basic Mappings ................................  168
     4          - Addressing ....................................  168
     5          - Detailed Mappings .............................  169



Kille                                                         [page 3]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     6          - Appendices ....................................  169














































Kille                                                         [page 4]


     Chapter 1 -- Overview



     1.1.  X.400

     This document relates primarily to the ITU 1988 and 1992 X.400
     Series Recommendations / ISO IEC 10021 on the Message Oriented
     Text Interchange Service (MOTIS).  This ISO/ITU standard is
     referred to in this document as "X.400", which is a convenient
     shorthand.  Any reference to the 1984 ITU Recommendations will be
     explicit.  Any mappings relating to elements which are in the
     1992 version and not in the 1988 version will be noted
     explicitly.  X.400 defines an Interpersonal Messaging System
     (IPMS), making use of a store and forward Message Transfer
     System.  This document relates to the IPMS, and not to wider       |
     application of X.400, such as EDI as defined in X.435.

     1.2.  RFC 822 and MIME

     RFC 822 evolved as a messaging standard on the DARPA (the US
     Defense Advanced Research Projects Agency) Internet.  RFC 822
     specifies an end to end message format, consisting of a header
     and an unstructured text body.   MIME (Multipurpose Internet Mail
     Extensions) specifies a structured message body format for use
     with RFC 822.  The term "RFC 822" is used in this document to
     refer to the combination of MIME and RFC 822. RFC 822 and MIME
     are used in conjunction with a number of different message
     transfer protocol environments.  The core of the MIXER
     specification is designed to work with any supporting message
     transfer protocol.

          One transfer protocol, SMTP, is of particular importance and
     is covered in MIXER.  On the Internet and other TCP/IP networks,
     RFC 822 is used in conjunction with
      RFC 821, also known as Simple Mail Transfer Protocol (SMTP)
     [31], in a manner conformant with the host requirements
     specification [10].  Use of MIXER with SMTP is defined in
     Appendix A.




Kille                                                         [page 6]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     1.3.  The need for conversion

     There is a large community using RFC 822 based protocols for mail
     services, who will wish to communicate with users of the IPMS
     provided by X.400 systems.  This will also be a requirement in
     cases where communities intend to make a transition to use of an
     X.400 IPMS, as conversion will be needed to ensure a smooth
     service transition.  It is expected that there will be more than
     one gateway, and this specification will enable them to behave in
     a consistent manner.  Note that the term gateway is used to
     describe a component performing the protocol mappings between RFC
     822 and X.400.  This is standard usage amongst mail implementors,
     but should be noted carefully by transport and network service
     implementors.

     Consistency between gateways is desirable to provide:

     1.   Consistent service to users.

     2.   The best service in cases where a message passes through
          multiple gateways.

     1.4.  General approach

     There are a number of basic principles underlying the details of
     the specification.  These principles are goals, and are not
     achieved in all aspects of the specification.

     1.   The specification should be pragmatic.  There should not be
          a requirement for complex mappings for "Academic" reasons.
          Complex mappings should not be required to support trivial
          additional functionality.

     2.   Subject to 1), functionality across a gateway should be as
          high as possible.

     3.   It is always a bad idea to lose information as a result of
          any transformation.  Hence, it is a bad idea for a gateway
          to discard information in the objects it processes.  This
          includes requested services which cannot be fully mapped.

     4.   All mail gateways actually operate at exactly one level
          above the layer on which they conceptually operate.  This
          implies that the gateway must not only be cognisant of the



Kille                                                         [page 7]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          semantics of objects at the gateway level, but also be
          cognisant of higher level semantics.  If meaningful
          transformation of the objects that the gateway operates on
          is to occur, then the gateway needs to understand more than
          the objects themselves.

     5.   Subject to 1), the specification should be reversible.  That
          is, a double transformation should bring you back to where
          you started.

     1.5.  Gatewaying Model

     1.5.1.  X.400

     X.400 defines the IPMS Abstract Service in X.420/ISO 10021-7 ,
     [11] which comprises of three basic services:

     1.   Origination

     2.   Reception

     3.   Management

     Management is a local interaction between the user and the IPMS,
     and is therefore not relevant to gatewaying.  The first two
     services consist of operations to originate and receive the
     following two objects:

     1.   IPM (Interpersonal Message). This has two components: a
          heading, and a body.  The body is structured as a sequence
          of body parts, which may be basic components (e.g., IA5
          text, or G3 fax), or Interpersonal Messages.  The heading
          consists of fields containing end to end user information,
          such as subject, primary recipients (To:), and importance.

     2.   IPN (Inter Personal Notification).  A notification  about
          receipt of a given IPM at the UA level.

     The Origination service also allows for origination of a probe,
     which is an object to test whether a given IPM could be correctly
     received.

     The Reception service also allows for receipt of Delivery Reports
     (DR), which indicate delivery success or failure.



Kille                                                         [page 8]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          These IPMS Services utilise the Message Transfer (MT)
     Abstract Service [12].  The MT Abstract Service provides the
     following three basic services:

     1.   Submission (used by IPMS Origination)

     2.   Delivery (used by IPMS Reception)

     3.   Administration (used by IPMS Management)

     Administration is a local issue, and so does not affect this
     standard.  Submission and delivery relate primarily to the MTS
     Message (comprising Envelope and Content), which carries an IPM
     or IPN (or other uninterpreted contents).  There is also an
     Envelope, which includes an ID, an originator, and a list of
     recipients.  Submission also includes the probe service, which
     supports the IPMS Probe. Delivery also includes Reports, which
     indicate whether a given MTS Message has been delivered or not.

          The MTS is provided by MTAs which interact using the MTA      |
     (Message Transfer Agent) Service, which defines the interaction
     between MTAs, along with the procedures for distributed
     operation.  This service provides for transfer of MTS Messages,
     Probes, and Reports.

     1.5.2.  RFC 822

     RFC 822 is based on the assumption that there is an underlying
     service, which is here called the 822-MTS service.  The 822-MTS
     service provides three basic functions:

     1.   Identification of a list of recipients.

     2.   Identification of an error return address.

     3.   Transfer of an RFC 822 message.

     It is possible to achieve 2) within the RFC 822 header.            |

          This specification will be used most commonly with SMTP as    |
     the 822-MTS service.  The core MIXER specification is written so   |
     that it does not rely on non-basic 822-MTS services.   Use of      |
     non-basic SMTP services is described in Appendix A.  The core of   |
     this document is written using SMTP terminology for 822-MTS        |



Kille                                                         [page 9]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     services, for clarity in its usual domain of application.          |

          An RFC 822 message consists of a header, and content which
     is uninterpreted ASCII text.  The header is divided into fields,
     which are the protocol elements.  Most of these fields are
     analogous to P2 heading fields, although some are analogous to
     MTS Service Elements or MTA Service Elements.

          RFC 822 supports delivery status notifications by use of the
     NOTARY mechanisms [29].

     1.5.3.  The Gateway

     Given this functional description of the two services, the
     functional nature of a gateway can now be considered.  It would    |
     be elegant to consider the SMTP (822-MTS) service mapping onto
     the MTS Service Elements and RFC 822 mapping onto an IPM, but
     reality just does not fit.  Another elegant approach would be to
     treat this document as the definition of an X.400 Access Unit
     (AU).  Again, reality does not fit.  It is necessary to consider
     that the IPM format definition, the IPMS Service Elements, the
     MTS Service Elements, and MTA Service Elements on one side are     |
     mapped into RFC 822 + SMTP on the other in a slightly tangled
     manner.  The details of the tangle will be made clear in Chapter
     5.  Access to the MTA Service Elements is minimised.

          The following basic mappings are thus defined.  When going
     from RFC 822 to X.400, an RFC 822 message and the associated SMTP  |
     information is always mapped into an IPM (MTA, MTS, and IPMS
     Services) and a Delivery Status Notification is mapped onto a
     Report.  Going from X.400 to RFC 822, an RFC 822 message and the   |
     associated SMTP information may be derived from:

     1.   An IPN (MTA, MTS, and IPMS services)

     2.   An IPM (MTA, MTS, and IPMS services)

     A Report (MTA, and MTS Services) is mapped onto a delivery status
     notification.

     Probes (MTA Service) must be processed by the gateway, as
     discussed in Chapter 5.  MTS Messages containing Content Types
     other than those defined by the IPMS are not mapped by the
     gateway, and should be rejected at the gateway.                    |



Kille                                                        [page 10]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          This specification is concerned with X.400 IPMS.  Future      |
     specifications may defined mappings for other X.400 content        |
     types.

     1.5.4.  Repeated Mappings

     The primary goal of this specification is to support single
     mappings, so that X.400 and RFC 822 users can communicate with
     maximum functionality.

          The mappings specified here are designed to work where a
     message traverses multiple times between X.400 and RFC 822. This
     is often essential, particularly in the case of distribution
     lists.  However, in general, this will lead to a level of service
     which is the lowest common denominator (approximately the
     services offered by RFC 822).

          Some RFC 822 networks may wish to use X.400 as an
     interconnection mechanism (typically for policy reasons), and
     this is fully supported.

          Where an X.400 message transfers to RFC 822 and then back to
     X.400, there is no expectation of X.400 services which do not
     have an equivalent service in standard RFC 822 being preserved -
     although this may be possible in some cases.

     1.6.  X.400 (1984)

     Much of this work is based on the initial specification of RFC
     987 and in its addendum RFC 1026, which defined a mapping between
     X.400(1984) and RFC 822.  A basic decision is that the mapping
     defined in this document is to the full 1988 version of X.400,
     and not to a 1984 compatible subset. New features of X.400(1988)
     can be used to provide a much cleaner mapping than that defined
     in RFC 987.  This is important, to give good support to
     communities which will utilise full X.400 at an early date.   To
     interwork with 1984 systems, Appendix B shall be followed.

          If a message is being transferred to an X.400(1984) system
     by way of X.400(1988) MTA it will give a slightly better service
     to follow the rules of Appendix B, than to downgrade without this
     knowledge.   Downgrading specifications which supplement those
     specified in X.400 are given in RFC 1328 and RFC 1496 (HARPOON)
     [6,23].



Kille                                                        [page 11]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     1.7.  X.400 (1992)

     X.400 (1992) features are not used by the core of this mapping,
     and so there is not an equivalent downgrade problem.

     1.8.  MIME

     MIME format messages are generated by this mapping.   As MIME
     messages are fully RFC 822 compliant, this will not cause
     problems with systems which are not MIME capable.

     1.9.  Body Parts

     MIME and X.400 IPMS can both carry arbitrary body parts.   This
     specification describes mapping of the framework for structured
     messages, but does not specify how specific body parts shall be
     mapped.   Body part mapping is an open ended problem, as new body
     parts (attachments) will continue to be added to both X.400 and
     MIME.

          MIME defines a mechanism for adding new body parts, and new
     body parts are registered with the IANA.

          X.400 defines a mechanism adding new body parts, usually
     referred to as Body Part 15.  Extensions are defined by Object
     Identifiers, so there is no requirement for a body part
     registration authority.   The Electronic Mail Association (EMA)
     maintains a list of some commonly used body parts.   The EMA has
     specified a mechanism to use the File Transfer Body Part (FTBP)
     as a more generic means to support message attachments.  This
     approach is gaining widespread commercial support.  MIXER defines
     how to map between MIME and both the Body Part 15 and EMA/FTBP
     extension mechanisms for X.400.   In many cases, this will enable
     a gateway implementor to map between the same body part carried
     by these mechanisms.

          Mapping of standard IPM and MIME body parts, and some
     extended MIME and X.400 body parts,  is defined in RFC 1494bis
     [7].  This also gives a model for specifying further mappings.

          It will not be possible to specify all mappings.  Therefore,
     MIXER defines encapsulation mechanisms for both MIME and X.400.
     This will allow all body parts to be transferred end to end,
     irrespective of a mapping being defined.



Kille                                                        [page 12]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          To provide a gateway service, it is therefore necessary for
     an implementation to conform to both this specification and to
     provide various body part mappings, such as those defined in RFC
     1494bis.

     1.10.  Compatibility with previous versions

     The changes between this and older versions of the document are
     given in Appendices H, I and J.    These are RFCs 987, 1026,       |
     1138, 1148 and 1327.  This document is a revision of RFC 1327 .   [
     As far as possible, changes have been made in a compatible        [
     fashion.                                                          [

     1.11.  Aspects not covered                                        [

     There have been a number of cases where previous versions of this |
     document were used in a manner which was not intended.  This      |
     section is to make clear some limitations of scope.  In
     particular, this specification does not specify:

     -    Extensions of RFC 822 to provide access to all X.400
          services

     -    X.400 user interface definition

     These are really coupled.  To map the X.400 services, this
     specification defines a number of extensions to RFC 822.  As a
     side effect, these give the 822 user access to SOME X.400
     services.  However, the aim on the RFC 822 side is to preserve
     current service, and it is intentional that access is not given
     to all X.400 services.  Thus, it will be a poor choice for X.400
     implementors to use MIXER  as an interface - there are too many
     aspects of X.400 which cannot be accessed through it.  If a text
     interface is desired, a specification targeted at X.400, without
     RFC 822 restrictions, would be more appropriate.  Some optional
     and limited extensions in this area have proved useful, and are
     defined in Appendix C.

     1.12.  Subsetting

     This proposal specifies a mapping which is appropriate to
     preserve services in existing RFC 822 communities.
     Implementations and specifications which subset this              |
     specification are non-conformant and strongly discouraged.



Kille                                                        [page 13]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     1.13.                                                             |
     Specification Language                                            |

     ISO and Internet standards have clear definitions as to the style |
     of language used.   This specification maps between  ISO/ITU      |
     protocol and Internet protocols.  This document uses ISO          |
     terminology for the following reasons:                            |

     1.   This was done in previous versions.                          |

     2.   ISO language may be mechanically converted to Internet       |
          language, but not vice versa.                                |

     To interpet this document according to Internet rules, replace    |
     every occurrence of "shall" with "must".                          |

     1.14.
     Related Specifications

     Mappings between Mail-11 and X.400 and Mail-11 and rfc822 are
     described in RFC1405, using mappings related to those defined
     here [3].

     1.15.  Document Structure

     This document has five chapters:

     1.   Overview - this chapter.

     2.   Service Elements - This describes the (end user) services
          mapped by a gateway.

     3.   Basic mappings - This describes some basic notation used in
          Chapters 3-5, the mappings between character sets, and some
          fundamental protocol elements.

     4.   Addressing - This considers the mapping between X.400 O/R
          names and RFC 822 addresses, which is a fundamental gateway
          component.

     5.   Detailed Mappings - This describes the details of all other
          mappings.

     There are also ten appendices.



Kille                                                        [page 14]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     WARNING:
          THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
          IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND
          X.400 (1988).  DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
          YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.

     1.16.  Acknowledgements

     The work in this specification was substantially based on RFC 987
     and RFC 1148, which had input from many people, who are credited
     in the respective documents.

          A number of comments from people on RFC 1148 lead to RFC
     1327.  In particular, there were comments and suggestions from:
     Maurice Abraham (HP); Harald Alvestrand (Sintef); Peter Cowen
     (X-Tel); Jim Craigie (JNT); Ella Gardner (MITRE); Christian
     Huitema (Inria); Erik Huizer (SURFnet); Neil Jones (DEC); Ignacio
     Martinez (IRIS); Julian Onions (X-Tel); Simon Poole (SWITCH);
     Clive Roberts (Data General); Pete Vanderbilt (SUN); Alan Young
     (Concurrent).

          RFC 1327 has been widely adopted, and a review team was
     formed.   This comprised of:  Urs Eppenberger (SWITCH)(Chair);
     Claudio Allocchio (INFN); Harald Alvestrand (UNINETT); Dave
     Crocker (Brandenburg); Ned Freed (Innosoft); Erik Huizer
     (SURFnet); Steve Kille (ISODE Consortium); Peter Sylvester
     (EdelWeb)

          Harald Alvestrand also supplied the tables mapping DSN
     status codes with X.400 codes.  Ned Freed defined parts of the
     File Transfer Body Part mapping.

          Comment and input has also been received from:  Samir        |
     Albadine (Transpac); Jacqui Caren (Cray); Allan Cargille (MCI);   |
     Kevin Carrosso (Innosoft); Eamon Doyle (Isocor); Jeroun Houttin
     (Terena); Jyrki Heikkinen (ICL); Kevin Jordan (CDS); Paul         |
     Kingsnorth (DEC); Carl-Uno Manros (Manros Consulting); Robert
     Miles (Softswitch); Michel Musy (Bull); Kenji Nonaka (NTT):  Tom  |
     Oliphant (SWITCH); Julian Onions (NEXOR); Mary la Roche           |
     (Citicorp); Eftimios Tsigros (Universite Libre de Bruxelles);     |
     David Wilson (ISODE Consortium); Alan Young (ISODE Consortium);






Kille                                                        [page 15]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Chapter 2 - Service Elements


     This chapter considers the services offered across a gateway
     built according to this specification.  It gives a view of the
     functionality provided by such a gateway for communication with
     users in the opposite domain.  This chapter considers service
     mappings in the context of SINGLE transfers only, and not
     repeated mappings through multiple gateways.


     2.1.  The Notion of Service Across a Gateway

     RFC 822 and X.400 provide a number of services to the end user.
     This chapter describes the extent to which each service can be
     supported across an X.400 <-> RFC 822 gateway.  The cases
     considered are single transfers across such a gateway, although
     the problems of multiple crossings are noted where appropriate.

     2.1.1.  Origination of Messages

     When a user originates a message, a number of services are
     available.  Some of these imply actions (e.g., delivery to a
     recipient), and some are insertion of known data (e.g.,
     specification of a subject field).  This chapter describes, for
     each offered service, to what extent it is supported for a
     recipient accessed through a gateway.  There are three levels of
     support:

     Supported
          The corresponding protocol elements map well, and so the
          service can be fully provided.

     Not Supported
          The service cannot be provided, as there is a complete
          mismatch.

     Partial Support
          The service can be partially fulfilled.

     In the first two cases, the service is simply marked as
     "Supported" or "Not Supported".  Some explanation may be given if
     there are additional implications, or the (non) support is not
     intuitive.  For partial support, the level of partial support is



Kille                                                        [page 16]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     summarised.  Where partial support is good,  this will be
     described by a phrase such as "Supported by use of.....".  A
     common case of this is where the service is mapped onto a non-
     standard service on the other side of the gateway, and this would
     have lead to support if it had been a standard service.  In many
     cases, this is equivalent to support.  For partial support, an
     indication of the mechanism is given, in order to give a feel for
     the level of support provided.  Note that this is not a
     replacement for Chapter 5, where the mapping is fully specified.

          If a service is described as supported, this implies:

     -    Semantic correspondence.

     -    No (significant) loss of information.

     -    Any actions required by the service element.

     An example of a service gaining full support: If an RFC 822
     originator specifies a Subject:  field, this is considered to be
     supported, as an X.400 recipient will get a subject indication.

     In many cases, the required action will simply be to make the
     information available to the end user.  In other cases, actions
     may imply generating a delivery report.

          All RFC 822 services are supported or partially supported
     for origination.  The implications of non-supported X.400
     services is described under X.400.


     2.1.2.  Reception of Messages

     For reception, the list of service elements required to support
     this mapping is specified.  This is really an indication of what
     a recipient might expect to see in a message which has been
     remotely originated.

     2.2.  RFC 822

     RFC 822 does not explicitly define service elements, as distinct
     from protocol elements.  However, all of the RFC 822 header
     fields, with the exception of trace, can be regarded as
     corresponding to implicit RFC 822 service elements.



Kille                                                        [page 17]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     2.2.1.  Origination in RFC 822

     A mechanism of mapping, used in several cases, is to map the RFC
     822 header into a heading extension in the IPM (InterPersonal
     Message).  This can be regarded as partial support, as it makes
     the information available to any X.400 implementations which are
     interested in these services. Communities which require
     significant RFC 822 interworking are recommended to require that
     their X.400 User Agents are able to display these heading
     extensions.  Support for the various service elements (headers)
     is now listed.

     Date:
          Supported.

     From:
          Supported.  For messages where there is also a sender field,
          the mapping is to "Authorising Users Indication", which has
          subtly different semantics to the general RFC 822 usage of
          From:.

     Sender:
          Supported.

     Reply-To:
          Supported.

     To:  Supported.

     Cc:  Supported.

     Bcc: Supported.

     Message-Id:
          Supported.

     In-Reply-To:
          Supported, for a single reference.  Where multiple
          references are given, partial support is given by mapping to
          "Cross Referencing Indication".  This gives similar
          semantics.

     References:
          Supported.



Kille                                                        [page 18]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Keywords:
          Supported by use of a heading extension.

     Subject:
          Supported.

     Comments:
          Supported by use of a heading extension.

     Encrypted:
          Supported by use of a heading extension.

     Resent-*
          Supported by use of a heading extension.  Note that
          addresses in these fields are mapped onto text, and so are
          not accessible to the X.400 user as addresses.  In
          principle, fuller support would be possible by mapping onto
          a forwarded IP Message, but this is not suggested.

     Other Fields
          In particular X-* fields, and "illegal" fields in common
          usage (e.g., "Fruit-of-the-day:") are supported by use of
          heading extensions.

     MIME introduces the following headings, which are supported as
     follows:

     Content-Type:
          Supported.  The definition of MIME Content Type is somewhat
          like X.400 Encoded Information Type,  but has some aspects
          of X.400 Content Type.  The mapping is complex, but it will
          either be mapped to an equivalent X.400 piece of information
          or tunnelled by use of a special extended body part defined
          in RFC 1494bis.                                              |

     Content-Transfer-Encoding:
          Supported.  The encoding of the information in X.400 will be
          appropriate to the data being transferred.  The service is
          mapped in an appropriate manner.

     Content-ID:
          Supported in some cases.  Support depend on the body part
          and the mapping selected by the gateway.




Kille                                                        [page 19]


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MIXER                                                DRAFT Version 2.2


     Content-Description:
          Supported in some cases.  Support depend on the body part
          and the mapping selected by the gateway.

     MIME-Version:
          Supported by use of a heading extension.

     MIME, like RFC 822, does not explicitly define services.   It is
     useful in the service section to note support for MIME Content
     types that do not map directly to atomic body parts:

     multipart/mixed
          Supported.

     multipart/alternative
          Partially supported.  No data is lost. The fact that the
          body parts are alternatives is indicated in a heading
          extension, and there is no guarantee that this can be
          interpreted by an X.400 user agent, and by a subject line.

     multipart/digest
          Supported.

     multipart/parallel
          Partially supported.  No data is lost. The fact that the     |
          body parts are parallel is indicated in a heading extension,
          which may not be interpreted by an X.400 user agent, and by
          a subject line.

     multipart/unknown
          Supported.  Unknown semantics are not mapped.

     message/rfc822
          Supported.

     message/partial
          Supported by mapping of message fragments to X.400 messages.
          X.400 User Agents will not in general be able to
          automatically reassemble fragments.

     message/external-body
          Supported by incorporating the external body into the X.400
          message.




Kille                                                        [page 20]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     message/unknown
          Supported.  Unknown semantics are not mapped.

     other                                                             |











































Kille                                                        [page 21]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          Support for the other MIME content types (text, application,
          image, audio, video) is defined in RFC 1494bis, with a       |
          fallback mechanism for undefined an unrecognised types       |
          defined in MIXER.

     2.2.2.  Reception by RFC 822

     This considers reception by an RFC 822 User Agent of a message
     originated in an X.400 system and transferred across a gateway.
     The following standard services (headers) may be present in such
     a message:

     Date:

     From:

     Sender:

     Reply-To:

     To:

     Cc:

     Bcc:

     Message-Id:

     In-Reply-To:

     References:

     Subject:

     Content-Type:

     Content-Transfer-Encoding:

     MIME-Version:








Kille                                                        [page 22]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     The following non-standard services (headers) may be present in
     the header of a message. These are defined in more detail in
     Chapter 5 (5.3.4, 5.3.6, 5.3.7):

     Autoforwarded:

     Autosubmitted:

     X400-Content-Identifier:

     Content-Language:

     Conversion:

     Conversion-With-Loss:

     Delivery-Date:

     Discarded-X400-IPMS-Extensions:

     Discarded-X400-MTS-Extensions:

     DL-Expansion-History:

     Deferred-Delivery:

     Expiry-Date:

     Importance:

     Incomplete-Copy:

     Latest-Delivery-Time:

     Message-Type:

     Obsoletes:

     Original-Encoded-Information-Types:

     Originator-Return-Address:

     Priority:




Kille                                                        [page 23]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Reply-By:

     Requested-Delivery-Method:

     Sensitivity:

     X400-Content-Type:

     X400-MTS-Identifier:

     X400-Originator:

     X400-Received:

     X400-Recipients:

     2.3.  X.400

     2.3.1.  Origination in X.400

     When mapping services from X.400 to RFC 822 which are not
     supported by RFC 822, new RFC 822 headers are defined, and        |
     registered by publication in this standard. It is intended that   |
     co-operating RFC 822 systems may also use them.  Where these new
     fields are used, and no system action is implied, the service can
     be regarded as being partially supported.  Chapter 5 describes
     how to map X.400 services onto these new headers.  Other elements
     are provided, in part, by the gateway as they cannot be provided
     by RFC 822.

          Some service elements are marked N/A (not applicable).
     There are five cases, which are marked with different comments:

     N/A (local)
          These elements are only applicable to User Agent / Message
          Transfer Agent interaction and so they cannot apply to RFC
          822 recipients.

     N/A (PDAU)
          These service elements are only applicable where the
          recipient is reached by use of a Physical Delivery Access
          Unit (PDAU), and so do not need to be mapped by the gateway.

     N/A (reception)



Kille                                                        [page 24]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          These services  are only applicable for reception.

     N/A (prior)
          If requested, this service must be performed prior to the
          gateway.

     N/A (MS)
          These services are only applicable to Message Store (i.e., a
          local service).

          Finally, some service elements are not supported.  In
     particular, the new security services are not mapped onto RFC
     822.  Unless otherwise indicated, the behaviour of service
     elements marked as not supported will depend on the criticality
     marking supplied by the user.  If the element is marked as
     critical for transfer or delivery, a non-delivery notification
     will be generated.  Otherwise, the service request will be
     ignored.

     2.3.1.1.  Basic Interpersonal Messaging Service

     These are the mandatory IPM services as listed in Section 19.8 of
     X.400 / ISO/IEC 10021-1, listed here in the order given. Section
     19.8 has cross references to short definitions of each service.

     Access management
          N/A (local).

     Content Type Indication
          Supported by a new RFC 822 header (X400-Content-Type:).      |

     Converted Indication
          Supported by a new RFC 822 header (X400-Received:).

     Delivery Time Stamp Indication
          N/A (reception).

     IP Message Identification
          Supported.

     Message Identification
          Supported, by use of a new RFC 822 header
          (X400-MTS-Identifier).  This new header is required, as
          X.400 has two message-ids whereas RFC 822 has only one (see



Kille                                                        [page 25]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          IP Message Identification

     Non-delivery Notification
          Not supported in all cases.  Supported where the recipient
          system supports NOTARY DSNs.  In general all RFC 822 systems
          will return error reports by use of IP messages.  In other
          service elements, this pragmatic result can be treated as
          effective support of this service element.

     Original Encoded Information Types Indication
          Supported as a new RFC 822 header
          (Original-Encoded-Information-Types:).

     Submission Time Stamp Indication
          Supported.

     Typed Body
          The mapping of ForwardedIPMessage and IA5 body parts is
          defined and supported.  A framework form mapping other body
          parts, including encapsulation mechanism is defined.
          Mapping of standard body parts and selected other body parts
          is defined in RFC 1494bis.

     User Capabilities Registration
          N/A (local).

     2.3.1.2.  IPM Service Optional User Facilities

     This section describes support for the optional (user selectable)
     IPM services as listed in Section 19.9 of X.400 / ISO/IEC 10021-
     1, listed here in the order given.  Section 19.9 has cross
     references to short definitions of each service.

     Additional Physical Rendition
          N/A (PDAU).

     Alternate Recipient Allowed
          Not supported.  There is no RFC 822 service equivalent to
          prohibition of alternate recipient assignment (e.g., an RFC
          822 system may freely send an undeliverable message to a
          local postmaster).  Thus, the gateway cannot prevent
          assignment of alternative recipients on the RFC 822 side.
          This service really means giving the user control as to
          whether or not an alternate recipient is allowed. This



Kille                                                        [page 26]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          specification requires transfer of messages to RFC 822
          irrespective of this service request, and so this service is
          not supported.

     Authorising User's Indication
          Supported.

     Auto-forwarded Indication
          Supported as new RFC 822 header (Auto-Forwarded:).

     Basic Physical Rendition
          N/A (PDAU).

     Blind Copy Recipient Indication
          Supported.

     Body Part Encryption Indication
          Supported by use of a new RFC 822 header
          (Original-Encoded-Information-Types:), although in most
          cases it will not be possible to map the body part in
          question.

     Content Confidentiality
          Not supported.

     Content Integrity
          Not supported.

     Conversion Prohibition
          Supported. Operation defined in RFC 1494bis.                 |

     Conversion Prohibition in Case of Loss of Information
          Supported.  Operation defined in RFC 1494bis.                |

     Counter Collection
          N/A (PDAU).

     Counter Collection with Advice
          N/A (PDAU).

     Cross Referencing Indication
          Supported.

     Deferred Delivery



Kille                                                        [page 27]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          N/A (prior).  This service should always be provided by the
          MTS prior to the gateway.  A new RFC 822 header
          (Deferred-Delivery:) is provided to transfer information on
          this service to the recipient.

     Deferred Delivery Cancellation
          N/A (local).

     Delivery Notification
          Supported.  This is performed at the gateway, but may be
          performed at the end system if the end system supports
          NOTARY.  Thus, a notification is sent by the gateway to the
          originator.                                                  *

     Delivery via Bureaufax Service
          N/A (PDAU).

     Designation of Recipient by Directory Name
          N/A (local).

     Disclosure of Other Recipients
          Supported by use of a new RFC 822 header (X400-Recipients:).
          This is descriptive information for the RFC 822 recipient,
          and is not reverse mappable.

     DL Expansion History Indication
          Supported by use of a new RFC 822 header
          (DL-Expansion-History:).

     DL Expansion Prohibited
          Distribution List means MTS supported distribution list, in
          the manner of X.400.  This service does not exist in the RFC
          822 world.  RFC 822 distribution lists should be regarded in |
          X.400 terms as an informal redistribution mechanism, beyond
          the scope of this control.  Messages will be sent to RFC 822 |
          distribution lists, irrespective of whether this service is  |
          requested.  Theoretically therefore, this service is         |
          supported, although in practice it is not supported.

     Express Mail Service
          N/A (PDAU).

     Expiry Date Indication
          Supported as new RFC 822 header (Expiry-Date:).  In general,



Kille                                                        [page 28]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          no automatic action can be expected.

     Explicit Conversion
          N/A (prior).

     Forwarded IP Message Indication
          Supported.                                                   |

     Grade of Delivery Selection
          Not Supported.  There is no equivalent service in RFC 822.   |

     Importance Indication
          Supported as new RFC 822 header (Importance:).

     Incomplete Copy Indication
          Supported as new RFC 822 header (Incomplete-Copy:).

     Language Indication
          Supported as new RFC 822 header (Language:).

     Latest Delivery Designation
          Not supported.  A new RFC 822 header (Latest-Delivery-Time:)
          is provided, which may be used by the recipient.

     Message Flow Confidentiality
          Not supported.

     Message Origin Authentication
          N/A (reception).

     Message Security Labelling
          Not supported.

     Message Sequence Integrity
          Not supported.

     Multi-Destination Delivery
          Supported.

     Multi-part Body
          Supported.

     Non Receipt Notification Request
          Not supported.



Kille                                                        [page 29]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Non Repudiation of Delivery
          Not supported.

     Non Repudiation of Origin
          N/A (reception).

     Non Repudiation of Submission
          N/A (local).

     Obsoleting Indication
          Supported as new RFC 822 header (Obsoletes:).

     Ordinary Mail
          N/A (PDAU).

     Originator Indication
          Supported.

     Originator Requested Alternate Recipient
          Not supported, but is placed as comment next to address
          (X400-Recipients:).

     Physical Delivery Notification by MHS
          N/A (PDAU).

     Physical Delivery Notification by PDS
          N/A (PDAU).

     Physical Forwarding Allowed
          Supported by use of a comment in a new RFC 822 header
          (X400-Recipients:), associated with the recipient in
          question.

     Physical Forwarding Prohibited
          Supported by use of a comment in a new RFC 822 header
          (X400-Recipients:), associated with the recipient in
          question.

     Prevention of Non-delivery notification
          Supported where SMTP and NOTARY are available.  In other     |
          cases formally supported, as delivery notifications cannot   |
          be generated by RFC 822.  In practice, errors will be
          returned as IP Messages, and so this service may appear not
          to be supported (see Non-delivery Notification).



Kille                                                        [page 30]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Primary and Copy Recipients Indication
          Supported

     Probe
          Supported at the gateway (i.e., the gateway services the
          probe).

     Probe Origin Authentication
          N/A (reception).

     Proof of Delivery
          Not supported.

     Proof of Submission
          N/A (local).

     Receipt Notification Request Indication
          Not supported.                                               |

     Redirection Disallowed by Originator                              |
          Redirection means MTS supported redirection, in the manner
          of X.400.  This service does not exist in the RFC 822 world.
          RFC 822 redirection (e.g., aliasing) should be regarded as
          an informal redirection mechanism, beyond the scope of this
          control.  Messages will be sent to RFC 822, irrespective of  |
          whether this service is requested. In practice, control of   |
          this service is not supported.

     Registered Mail
          N/A (PDAU).

     Registered Mail to Addressee in Person
          N/A (PDAU).

     Reply Request Indication
          Supported as comment next to address.

     Replying IP Message Indication
          Supported.

     Report Origin Authentication
          N/A (reception).

     Request for Forwarding Address



Kille                                                        [page 31]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          N/A (PDAU).

     Requested Delivery Method
          N/A (local).   The services required must be dealt with at
          submission time.  Any such request is made available through
          the gateway by use of a comment associated with the
          recipient in question.

     Return of Content
          Supported where SMTP and NOTARY are used. In principle for   |
          other situations, this is N/A, as non-delivery notifications |
          are not supported.  In practice, most RFC 822 systems will
          return part or all of the content along with the IP Message
          indicating an error (see Non-delivery Notification).

     Sensitivity Indication
          Supported as new RFC 822 header (Sensitivity:).

     Special Delivery
          N/A (PDAU).

     Stored Message Deletion
          N/A (MS).

     Stored Message Fetching
          N/A (MS).

     Stored Message Listing
          N/A (MS).

     Stored Message Summary
          N/A (MS).

     Subject Indication
          Supported.

     Undeliverable Mail with Return of Physical Message
          N/A (PDAU).

     Use of Distribution List
          In principle this applies only to X.400 supported
          distribution lists (see DL Expansion Prohibited).
          Theoretically, this service is N/A (prior).  In practice,
          because of informal RFC 822 lists, this service can be



Kille                                                        [page 32]


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MIXER                                                DRAFT Version 2.2


          regarded as supported.

     Auto-Submitted Indication
          Supported

     2.3.2.  Reception by X.400

     2.3.2.1.  Standard Mandatory Services

     The following standard IPM mandatory  user facilities are
     required for reception of RFC 822 originated mail by an X.400 UA.


     Content Type Indication

     Delivery Time Stamp Indication

     IP Message Identification

     Message Identification

     Non-delivery Notification

     Original Encoded Information Types Indication

     Submission Time Stamp Indication

     Typed Body

     2.3.2.2.  Standard Optional Services

     The following standard IPM optional user facilities are required
     for reception of RFC 822 originated mail by an X.400 UA.

     Authorising User's Indication

     Blind Copy Recipient Indication

     Cross Referencing Indication

     Originator Indication

     Primary and Copy Recipients Indication




Kille                                                        [page 33]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Replying IP Message Indication

     Subject Indication

     2.3.2.3.  New Services

     A new X.400 service "RFC 822 Header Field" is defined using the   |
     extension facilities.  This allows for any RFC 822 header field
     to be represented.  It may be present in RFC 822 originated       |
     messages which are received by an X.400 UA.





































Kille                                                        [page 34]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Chapter 3 Basic Mappings



     3.1.  Notation

     The X.400 protocols are encoded in a structured manner according
     to ASN.1, whereas RFC 822 is text encoded.  To define a detailed
     mapping, it is necessary to refer to detailed protocol elements
     in each format.  A notation to achieve this is described in this
     section.


     3.1.1.  RFC 822

     Structured text is defined according to the Extended Backus Naur
     Form (EBNF) defined in Section 2 of RFC 822 [16].  In the EBNF
     definitions used in this specification, the syntax rules given in
     Appendix D of RFC 822 are assumed.  When these EBNF tokens are
     referred to outside an EBNF definition, they are identified by
     the string "822." appended to the beginning of the string (e.g.,
     822.addr-spec).  Additional syntax rules, to be used throughout
     this specification, are defined in this chapter.

     The EBNF is used in two ways.

     1.   To describe components of RFC 822 messages (or of SMTP       |
          components).  When these new EBNF tokens are referred to
          outside an EBNF definition, they are identified by the
          string "EBNF." appended to the beginning of the string
          (e.g., EBNF.importance).

     2.   To describe the structure of IA5 or ASCII information not in
          an RFC 822 message.

     For all new EBNF, tokens will either be self delimiting, or be
     delimited by self delimiting tokens.  Comments and LWSP are not
     used as delimiters, except for the following cases, where LWSP
     may be inserted according to RFC 822 rules.

     -    Around the ":" in all headers

     -    EBNF.labelled-integer




Kille                                                        [page 35]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     -    EBNF.object-identifier

     -    EBNF.encoded-info

     RFC 822 folding rules are applied to all headers.  Comments are
     never used in these new headers.

          This notation is used in a modified form to refer to NOTARY
     ENBF [29].  For this EBNF, the keyword EBNF it replaces with DSN, |
     for example DSN.final-recipient-field fields.

     3.1.2.  ASN.1

     An element is referred to with the following syntax, defined in
     EBNF:

             element         = service "." definition *( "." definition )
             service         = "IPMS" / "MTS" / "MTA"
             definition      = identifier / context
             identifier      = ALPHA *< ALPHA or DIGIT or "-" >
             context         = "[" 1*DIGIT "]"

     The EBNF.service keys are shorthand for the following service
     specifications:

     IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO
          10021-7.

     MTS  MTSAbstractService defined in Section 9 of X.411 / ISO
          10021-4.

     MTA  MTAAbstractService defined in Section 13 of X.411 / ISO
          10021-4.

     FTBP File Transfer Body Part, as defined in [28].  LP The first
          EBNF.identifier identifies a type or value key in the
          context of the defined service specification.   Subsequent
          EBNF.identifiers identify a value label or type in the
          context of the first identifier (SET or SEQUENCE).
          EBNF.context indicates a context tag, and is used where
          there is no label or type to uniquely identify a component.
          The special EBNF.identifier keyword "value" is used to
          denote an element of a sequence.




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     For example, IPMS.Heading.subject defines the subject element of
     the IPMS heading.  The same syntax is also used to refer to
     element values.  For example,
     MTS.EncodedInformationTypes.[0].g3Fax refers to a value of
     MTS.EncodedInformationTypes.[0] .

     3.2.  ASCII and IA5

     A gateway will interpret all IA5 as ASCII.  Thus, mapping between
     these forms is conceptual.

     3.3.  Standard Types

     There is a need to convert between ASCII text and some of the     |
     types defined in ASN.1 [14].  For each case, an EBNF syntax
     definition is given, for use in all of this specification, which
     leads to a mapping between ASN.1, and an EBNF construct.  All
     EBNF syntax definitions of ASN.1 types are in lower case, whereas
     ASN.1 types are referred to with the first letter in upper case.
     Except as noted, all mappings are symmetrical.

     3.3.1.  Boolean

     Boolean is encoded as:

             boolean = "TRUE" / "FALSE"


     3.3.2.  NumericString

     NumericString is encoded as:

             numericstring = *DIGIT


     3.3.3.  PrintableString

     PrintableString is a restricted IA5String defined as:

             printablestring  = *( ps-char )
             ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                                / "," / "-" / "." / "/" / ":" / "=" / "?"
             ps-delim         = "(" / ")"
             ps-char          = ps-delim / ps-restricted-char



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     This can be used to represent real printable strings in EBNF.

     3.3.4.  T.61String

     In cases where T.61 strings are only used for conveying human
     interpreted information, the aim of a mapping is  to render the
     characters appropriately in the remote character set, rather than
     to maximise reversibility.  For these cases, there are two
     options, both of which are conformant to this specification:

     1.   The mappings to IA5 defined in ITU Recommendation X.408
          (1988) may be used [13].  These will then be encoded in
          ASCII.   This is the approach mandated in RFC 1327.

     2.   This mapping may be used if the characters are not contained
          within ASCII repertoire, but are all in an IANA-registered
          character set.  Use the encoding defined in RFC 1522 [9].    |
          to generate appropriate encoded-words.  If this mapping is   |
          used, the character set ISO-8859-1 shall be used if all of   |
          the characters needed are available in this repertoire.  In  |
          other cases, the character set TELETEX shall be used.  The   |
          details of these mappings are defined in the Appendix of     |
          RFC1494bis.

          There is also a need to represent Teletex Strings in ASCII,
     for some aspects of O/R Address.  For these, the following
     encoding is used:

             teletex-string   = *( ps-char / t61-encoded )
             t61-encoded      = "{" 1* t61-encoded-char "}"
             t61-encoded-char = 3DIGIT

     Characters in EBNF.ps-char are mapped simply.  Other octets,      |
     including control characters,  are mapped using a quoting
     mechanism similar to the printable string mechanism.  Each octet
     is represented as 3 decimal digits.

     There are a number of places where a string may have a Teletex
     and/or Printable String representation.  The following BNF is
     used to represent this.

             teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]

     The natural mapping is restricted to EBNF.ps-char, in order to



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     make the full BNF easier to parse.

     3.3.5.  UTCTime

     Both UTCTime and the RFC 822 822.date-time syntax contain:  Year
     (lowest two digits), Month, Day of Month, hour, minute, second
     (optional), and Timezone.  822.date-time also contains an
     optional day of the week, but this is redundant.  Therefore a
     symmetrical mapping can be made between these constructs.

     Note:
          In practice, a gateway will need to parse various illegal
          variants on 822.date-time.  In cases where 822.date-time
          cannot be parsed, it is recommended that the derived UTCTime
          is set to the value at the time of translation.

     When mapping to X.400, the UTCTime format which specifies the
     timezone offset shall be used.

     When mapping to RFC 822, the 822.date-time format shall include a
     numeric timezone offset (e.g., +0000).

     When mapping time values, the timezone shall be preserved as
     specified.  The date shall not be normalised to any other
     timezone.

     3.3.6.  Integer

     A basic ASN.1 Integer will be mapped onto EBNF.numericstring.  In
     many cases ASN.1 will enumerate Integer values or use ENUMERATED.
     An EBNF encoding labelled-integer is provided. When mapping from
     EBNF to ASN.1, only the integer value is mapped, and the
     associated text is discarded.  When mapping from ASN.1 to EBNF,
     addition of an appropriate text label is strongly encouraged.

             labelled-integer ::= [ key-string ] "(" numericstring ")"

             key-string      = *key-char
             key-char        = <a-z, A-Z, 0-9, and "-">


     3.3.7.  Object Identifier

     Object identifiers are represented in a form similar to that



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     given in ASN.1.  The order is the same as for ASN.1 (big-endian).
     The numbers are mandatory, and used when mapping from the ASCII
     to ASN.1.  The key-strings are optional.  It is recommended that
     as many strings as possible are generated when mapping from ASN.1
     to ASCII, to facilitate user recognition.

             object-identifier  ::= oid-comp object-identifier
                             | oid-comp

             oid-comp ::= [ key-string ] "(" numericstring ")"

     An example representation of an object identifier is:

             joint-iso-ccitt(2) mhs (6) ipms (1) ep (11) ia5-text (0)

             or

             (2) (6) (1)(11)(0)

     Because of the use of brackets and the conflict with the RFC 822  |
     comment convention, this syntax is not used in structures fields.

     3.4.  Encoding ASCII in Printable String

     Some information in RFC 822 is represented in ASCII, and needs to
     be mapped into X.400 elements encoded as printable string.  For
     this reason, a mechanism to represent ASCII encoded as
     PrintableString is needed.

          A structured subset of EBNF.printablestring is now defined.
     This shall be used to encode ASCII in the PrintableString
     character set.

             ps-encoded       = *( ps-restricted-char / ps-encoded-char )
             ps-encoded-char  = "(a)"               ; (@)
                              / "(p)"               ; (%)
                              / "(b)"               ; (!)
                              / "(q)"               ; (")
                              / "(u)"               ; (_)
                              / "(l)"               ; "("
                              / "(r)"               ; ")"
                              / "(" 3DIGIT ")"

     The 822.3DIGIT in EBNF.ps-encoded-char must have range 0-127, and



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     is interpreted in decimal as the corresponding ASCII character.
     Special encodings are given for: at sign (@), percent (%),
     exclamation mark/bang (!), double quote ("), underscore (_), left
     bracket ((), and right bracket ()).  These characters, with the
     exception of round brackets, are not included in PrintableString,
     but are common in RFC 822 addresses.  The abbreviations will ease
     specification of RFC 822 addresses from an X.400 system.  These
     special encodings shall be interpreted in a case insensitive
     manner, but always generated in lower case.

          A reversible mapping between PrintableString and ASCII can
     now be defined.  The reversibility means that some values of
     printable string (containing round braces) cannot be generated
     from ASCII.  Therefore, this mapping must only be used in cases
     where the printable strings may only be derived from ASCII (and
     will therefore have a restricted domain).  For example, in this
     specification, it is only applied to a Domain Defined Attribute
     which will have been generated by use of this specification and a
     value such as "(" would not be possible.

          To encode ASCII as PrintableString, the EBNF.ps-encoded
     syntax is used, with all EBNF.ps-restricted-char mapped directly.
     All other 822.CHAR are encoded as EBNF.ps-encoded-char.

          To encode PrintableString as ASCII, parse PrintableString as
     EBNF.ps-encoded, and then reverse the previous mapping.  If the
     PrintableString cannot be parsed, then the mapping is being
     applied in to an inappropriate value, and an error shall be given
     to the procedure doing the mapping. In some cases, it may be
     preferable to pass the printable string through unaltered.

     Some examples are now given.  Note the arrows which indicate
     asymmetrical mappings:

                     PrintableString           ASCII

                     'a demo.'         <->   'a demo.'
                     foo(a)bar         <->   foo@bar
                     (q)(u)(p)(q)      <->   "_%"
                     (a)               <->   @
                     (A)               ->    @
                     (l)a(r)           <->   (a)
                     (126)             <->   ~
                     (                 ->    (



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                     (l)               <->   (


     3.5.  RFC 1522

     RFC 1522 defines a mechanism for encoding other character set
     information into elements of RFC 822 Headers.   A gateway may
     ignore this encoding and treat the elements as ASCII.

          A preferred approach is for the gateway to interpret the RFC
     1522 encoding. This will not always be straightforward, because:

     1.   RFC 1522 permits an openly extensible character set choice,
          which may be broader than T.61.

     2.   It may not be possible to map all characters into the
          equivalent X.400 field.

     RFC 1522 is only applied to fields which are "for information
     only".  A gateway which interprets header elements according to
     RFC 1522 may apply reasonable heuristics to minimise information
     loss.

























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     Chapter 4 - Addressing and Message IDs


     Addressing is the most complex aspect of X.400 <-> RFC 822
     gateway and is therefore  given a separate chapter.  This chapter
     also discusses message identifiers, as they are closely linked to
     addresses.  This chapter, as a side effect, also defines a
     textual representation of an X.400 O/R Address.   This
     specification has much similarity to the X.400(92) representation
     of addresses.   This was because early versions of this
     specification were a major input to this work.  This
     specification retains compatibility with earlier versions.  The   |
     the X.400 specification of address representation can be parsed   |
     but is not generated.

          Initially we consider an address in the (human) mail user
     sense of "what is typed at the mailsystem to reference a mail
     user".  A basic RFC 822 address is defined by the EBNF
     EBNF.822-address:

             822-address     = [ route ] addr-spec

     In SMTP (or another 822-MTS protocol), the originator and each    |
     recipient are considered to be defined by such a construct.  In
     an RFC 822 header, the EBNF.822-address is encapsulated in the
     822.address syntax rule, and there may also be associated
     comments.  None of this extra information has any semantics,
     other than to the end user.

          The basic X.400 O/R Address, used by the MTS for routing, is
     defined by MTS.ORAddress.  In IPMS, the MTS.ORAddress is
     encapsulated within IPMS.ORDescriptor.

          It can be seen that RFC 822 822.address must be mapped with
     IPMS.ORDescriptor, and that RFC 822 EBNF.822-address must be
     mapped with MTS.ORAddress.

          Section 4.1 defines a textual representation of an O/R
     Address, which is used throughout the rest of this specification.
     This text representation is designed to represent an X.400
     address in the LHS (local part) of an RFC 822 address, and so
     this representation gives a mechanism to represent X.400          |
     addresses within RFC 822 addresses.




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          Section 4.2 describes a global equivalence mapping between
     parts of the X.400 and RFC 822 name spaces, which gateways
     conforming to this specification must support.

          Section 4.3 is the core part of this chapter, and defines
     the mapping mechanism.


     4.1.  A textual representation of MTS.ORAddress

     MTS.ORAddress is structured as a set of attribute value pairs.
     It is clearly necessary to be able to encode this in ASCII for
     gatewaying purposes.  All components shall be encoded, in order
     to guarantee return of error messages, and to optimise third
     party replies.

     4.1.1.  Basic O/R Address Representation

     An O/R Address has a number of structured and unstructured
     attributes.  For each unstructured attribute, a key and an
     encoding is specified.  For structured attributes, the X.400
     attribute is mapped onto one or more attribute value pairs.  For
     domain defined attributes, each element of the sequence will be
     mapped onto a triple (key and two values), with each value having
     the same encoding.  The attributes are as follows, with 1984
     attributes given in the first part of the table.  For each
     attribute, a reference is given, consisting of the relevant
     sections in X.402 / ISO 10021-2, and the extension identifier for
     88 only attributes:

       Attribute (Component)                 Key         Enc     Ref     Id

84/88 Attributes

MTS.CountryName                        C                 P     18.3.3
MTS.AdministrationDomainName           ADMD              P     18.3.1
MTS.PrivateDomainName                  PRMD              P     18.3.21
MTS.NetworkAddress                     X121              N     18.3.7
MTS.TerminalIdentifier                 T-ID              P     18.3.23
MTS.OrganizationName                   O                 P/T   18.3.9
MTS.OrganizationalUnitNames.value      OU                P/T   18.3.10
MTS.NumericUserIdentifier              UA-ID             N     18.3.8
MTS.PersonalName                       PN                P/T   18.3.12
MTS.PersonalName.surname               S                 P/T   18.3.12



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MTS.PersonalName.given-name            G                 P/T   18.3.12
MTS.PersonalName.initials              I                 P/T   18.3.12
MTS.PersonalName
   .generation-qualifier               GQ                P/T   18.3.12
MTS.DomainDefinedAttribute.value       DD                P/T   18.1

88 Attributes

MTS.CommonName                         CN                P/T   18.3.2    1
MTS.TeletexCommonName                  CN                P/T   18.3.2    2
MTS.TeletexOrganizationName            O                 P/T   18.3.9    3
MTS.TeletexPersonalName                PN                P/T   18.3.12   4
MTS.TeletexPersonalName.surname        S                 P/T   18.3.12   4
MTS.TeletexPersonalName.given-name     G                 P/T   18.3.12   4
MTS.TeletexPersonalName.initials       I                 P/T   18.3.12   4
MTS.TeletexPersonalName
   .generation-qualifier               GQ                P/T   18.3.12   4
MTS.TeletexOrganizationalUnitNames
   .value                              OU                P/T   18.3.10   5
MTS.TeletexDomainDefinedAttribute
   .value                              DD                P/T   18.1      6
MTS.PDSName                            PD-SERVICE        P     18.3.11   7
MTS.PhysicalDeliveryCountryName        PD-C              P     18.3.13   8
MTS.PostalCode                         PD-CODE           P     18.3.19   9
MTS.PhysicalDeliveryOfficeName         PD-OFFICE         P/T   18.3.14   10
MTS.PhysicalDeliveryOfficeNumber       PD-OFFICE-NUM     P/T   18.3.15   11
MTS.ExtensionORAddressComponents       PD-EXT-ADDRESS    P/T   18.3.4    12
MTS.PhysicalDeliveryPersonName         PD-PN             P/T   18.3.17   13
MTS.PhysicalDeliveryOrganizationName   PD-O              P/T   18.3.16   14
MTS.ExtensionPhysicalDelivery
   AddressComponents                   PD-EXT-DELIVERY   P/T   18.3.5    15
MTS.UnformattedPostalAddress           PD-ADDRESS        UPA   18.3.25   16|
MTS.StreetAddress                      PD-STREET         P/T   18.3.22   17
MTS.PostOfficeBoxAddress               PD-BOX            P/T   18.3.18   18
MTS.PosteRestanteAddress               PD-RESTANTE       P/T   18.3.20   19
MTS.UniquePostalName                   PD-UNIQUE         P/T   18.3.26   20
MTS.LocalPostalAttributes              PD-LOCAL          P/T   18.3.6    21
MTS.ExtendedNetworkAddress
   .e163-4-address.number              NET-NUM           N     18.3.7    22
MTS.ExtendedNetworkAddress
   .e163-4-address.sub-address         NET-SUB           N     18.3.7    22
MTS.ExtendedNetworkAddress
   .psap-address                       NET-PSAP          X     18.3.7    22
MTS.TerminalType                       T-TY              I     18.3.24   23



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     The following keys identify different EBNF encodings, which are
     associated with the ASCII representation of MTS.ORAddress.

                        Key         Encoding

                        P     printablestring
                        N     numericstring
                        T     teletex-string
                        P/T   teletex-and-or-ps
                        UPA   upa-string                               |
                        I     labelled-integer
                        X     presentation-address

     The BNF for presentation-address is taken from the specification
      RFC 1278 "A String Encoding of Presentation Address" [24].

     In most cases, the EBNF encoding maps directly to the ASN.1
     encoding of the attribute.  There are a few exceptions. In cases
     where an attribute can be encoded as either a PrintableString or
     NumericString (Country, ADMD, PRMD), either form is mapped into
     the BNF.  When generating ASN.1, the NumericString encoding shall |
     be used if the string contains digits and only digits.

     There are a number of cases where the P/T (teletex-and-or-ps)
     representation is used.  Where the key maps to a single
     attribute, this choice is reflected in the encoding of the
     attribute (attributes 10-21).  For most of the 1984 attributes
     and common name, there is a printablestring and a teletex
     variant.   This pair of attributes is mapped onto the single
     component here.  This will give a clean mapping for the common
     cases where only one form of the name is used.                    |

     The Unformatted Postal Address has a slightly more complex        |
     mapping onto a variant of   (teletex-and-or-ps), defined as:      |

     upa-string = [ printable-upa ] [ "*" teletex-string ]
     printable-upa = printablestring *( "|" printablestring )

     The optional teletex part is straightforward.  There is an        |
     (optional) sequence of printable strings which are mapped in      |
     order.  For example:                                              |

     /PD-ADDRESS=The Dome|The Square|Richmond|England/




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          X.400 (1992) has introduced as string representation of O/R
     Addresses.  This has specified a number of string keywords for
     attributes.  As earlier versions of this specification  were an   |
     input to this work, many of the keywords are the same.  To
     increase compatibility, the following alternative values shall be
     recognised when mapping from RFC 822 to X.400.  These shall not
     be generated when mapping from X.400 to RFC 822.

                        Keyword         Alternative

                    ADMD              A
                    PRMD              P
                    GQ                Q
                    X121              X.121
                    UA-ID             N-ID
                    PD-OFFICE-NUM     PD-OFFICE NUMBER
                    PD-OFFICE-NUM     PD-OFN
                    PD-EXT-ADDRESS    PD-EA
                    PD-EXT-DELIVERY   PD-ED
                    PD-OFFICE         PD-OF
                    PD-STREET         PD-S
                    PD-UNIQUE         PD-U
                    PD-LOCAL          PD-L
                    PD-RESTANTE       PD-R
                    PD-BOX            PD-B
                    PD-CODE           PD-PC
                    PD-SERVICE        PD-SN
                    DD                DDA

     When mapping from RFC 822 to X.400, the keywords: OU1, OU2, OU3,
     and OU4, shall be recognised.  If these are present, no keyword
     OU shall be present.  These will be treated as ordered values of
     OU.  PD-A1, PD-A2, PD-A3, PD-A4, PD-A5, PD-A6 shall be treated as
     ordered lines.  If present, these will be assembled with
     separating line feeds to form a single physical address.  In this
     case PD-ADDRESS shall not be present.

          If ISDN is present, is may be interpreted as an E.163/164
     address, using local heuristics to parse the string.  X.400
     defines the key, but does not give an interpretation of the
     value.

          For T-TY, the X.400 recommended values are preferred, but
     other values are allowed.  These values are: tlx (3); ttx (4);    |



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     g3fax (5); g4fax (6); ia5 (7); and vtx (8).

     4.1.2.  Encoding of Personal Name

     Handling of Personal Name and Teletex Personal Name based purely
     on the EBNF.standard-type syntax defined above is likely to be
     clumsy.  It seems desirable to utilise the "human" conventions
     for encoding these components.  A syntax is defined, which is
     designed to provide a clean encoding for the common cases of O/R
     Address specification where:

     1.   There is no generational qualifier

     2.   Initials, if present, contain only letters

     3.   Given Name, if present, does not contain full stop ("."),
          and is at least two characters long.

     4.   Surname does not contain full stop in the first two
          characters.

     5    If Surname is the only component, it does not contain full
          stop.

     The following EBNF is defined:

             encoded-pn      = [ given "." ] *( initial "." ) surname

             given           = 2*<ps-char not including ".">

             initial         = ALPHA

             surname         = printablestring

     This is used to map from any string containing only printable
     string characters to an O/R address personal name.  To map from a
     string to O/R Address components, parse the string according to
     the EBNF.  The given name and surname are assigned directly.  All
     EBNF.initial tokens are concatenated without intervening full
     stops to generate the initials component.

          For an O/R address which follows the above restrictions, a
     string is derived in the natural manner.  In this case, the




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     mapping will be reversible.

     For example:

             GivenName       = "Marshall"
             Surname         = "Rose"

             Maps with  "Marshall.Rose"

             Initials        = "MT"
             Surname         = "Rose"

             Maps with  "M.T.Rose"

             GivenName       = "Marshall"
             Initials        = "MT"
             Surname         = "Rose"

             Maps with  "Marshall.M.T.Rose"

     Note that X.400 suggests that Initials is used to encode ALL      |
     initials.  Therefore, the defined encoding is "natural" when
     either GivenName or Initials, but not both, are present.  The     |
     case where both are present can be encoded.

     4.1.3.  Standard Encoding of MTS.ORAddress

     Given this structure, we can specify a BNF representation of an   |
     O/R Address. The output format of addresses is defined by         |
     EBNF.std-or-address.  The more flexible input format is defined   |
     by EBNF.std-or-address-input. The input BNF has been added        |
     subsequent to RFC 1327, to reflect the formal incorporation of a  |
     number of heuristics.  The output format is used in all examples.

             std-or-address  = 1*( "/" attribute "=" value ) "/"        |
             attribute       = standard-type                            |
                             / "RFC-822"                                |
                             / registered-dd-type                       |
                             / dd-key "." std-printablestring           |








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             std-or-address-input = ( sep ) (pair) *( sep pair ) ( sep) |
             sep             = "/" / ";"                                |
             pair            = input-attribute "=" value                |
             input-attribute = attribute                                |
                             / dd-key ":" std-printablestring           |



             standard-type   = key-string

             registered-dd-type
                             = key-string dd-key          = key-string

             value           = std-printablestring

             std-printablestring
                             =  *(  std-char  /  std-pair  )  std-char
             =     <"{",     "}",     "*",     and     any     ps-char  |
                                              except  "/"  and  "="  >
             std-pair        = "$" ps-char

     The standard-type is any key defined in the table in Section 4.2,
     except PN, and DD.  The BNF leads to a set of attribute/value
     pairs. The value is interpreted according to the EBNF encoding
     defined in the table.

          If the standard-type is PN, the value is interpreted
     according to EBNF.encoded-pn, and the components of
     MTS.PersonalName and/or MTS.TeletexPersonalName derived
     accordingly.

          If dd-key is the recognised Domain Defined string (DD), then
     the type and value are interpreted according to the syntax
     implied from the encoding, and aligned to either the teletex or
     printable string form.  Key and value shall have the same
     encoding.

          If value is "RFC-822", then the (printable string) Domain
     Defined Type of "RFC-822" is assumed.  This is an optimised
     encoding of the domain defined type defined by this
     specification.

          The matching of all keywords shall be done in a case-



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     independent manner.

          EBNF.std-or-address uses the characters "/" and "=" as
     delimiters.  Domain Defined Attributes and any value may contain
     these characters.  A quoting mechanism, using the non-printable
     string "$" is used to allow these characters to be represented.

          If the value is registered-dd-type, and the value is
     registered at the Internet Assigned Numbers Authority (IANA) as
     an accepted Domain Defined Attribute type, then the value shall
     be interpreted accordingly.  This restriction maximises the
     syntax checking which can be done at a gateway.                   |

          If an address of this syntax is parsed, and a country value  |
     is present, but no ADMD, the string shall be interpreted as is an |
     ADMD value of single space had been specified.

     4.2.  Global Address Mapping

     From a user perspective, the ideal mapping  would be entirely
     symmetrical and global, to enable addresses to be referred to
     transparently in the remote system, with the choice of gateway
     being left to the Message Transfer Service.  There are two
     fundamental reasons why this is not possible:

     1.   The syntaxes are sufficiently different to make this
          impossible.

     2    There is insufficient administrative co-operation between
          the X.400 and RFC 822 name registration authorities for this
          to work.

     Another way to view this situation is to see that there is not a
     full global equivalence between X.400 and RFC 822 addressing.  To
     meet user needs to the extent possible, this specification
     provides for equivalence where there is sufficient co-operation.
     To be useful, this equivalence must be recognised and interpreted
     in the same way by all gateways.  Therefore, an asymmetrical
     mapping is defined, which can be symmetrical where there is
     appropriate administrative co-operation.  Section 4.3 describes
     consider the asymetrical aspects.   This section describes how
     the administrative co-ordination for symmetrical mappings is
     achieved.




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          In order to achieve a symmetrical mapping which is supported
     by all gateways which conform to this specification, there is a
     need to define an administrative equivalence between parts of the
     O/R Address and Domain namespaces.   This information is defined
     globally, and must be used by any gateway which conforms to this
     specification.  Currently, three ways are defined to access this
     mapping information.

     1.   Distribution of text tables.  This is described in Appendix
          F of this specification.

     2.   Distribution by Domain Name Service.   This is described in
          RFC 1664 [4].

     3.   Distribution by X.500 Directory Service.   This is defined
          in RFC tbs [27].

          The following sections define how the namespace equivalence
     is modelled.  The Internet Domain Namespace defines a simple
     hierarchy.   For the purposes of this mapping, only parts of the
     namespace where domains conform to the EBNF domain-syntax are
     allowed.

             domain-syntax   = alphanum [ *alphanumhyphen alphanum ]
             alphanum        = <ALPHA or DIGIT>
             alphanumhyphen  = <ALPHA or DIGIT or HYPHEN>


     Although RFC 822 allows for a more general syntax, this
     restricted syntax is chosen as it is the one chosen by the
     various domain service administrations.  In practice, it reflects
     all RFC 822 usage.

          The following O/R Address attributes are considered as a
     hierarchy, and may be specified by the domain.  They are (in
     order of the hierarchy defined by MIXER):

             Country, ADMD, PRMD, Organization, Organizational Unit

     There may be multiple Organizational Units.   This hierarchy
     reflects most usage of X.400, although X.400 may be used in other
     ways. In particular, it covers the Mnemonic O/R Address using a
     1984 compatible encoding.  This is seen as the dominant form of
     O/R Address. MIXER equivalence mappings may only be used when



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     this hierarchy applies.

          An equivalence mapping is defined between two nodes in the
     respective hierarchies. For example:

             => "AC.UK" might be mapped with
             C="GB", ADMD="GOLD 400", PRMD="UK.AC"

     The mapping identifies that the management of these points in the
     respective hierarchies is the same (or co-operate very closely).
     The equivalence means that the namespaces below this equivalence
     point map 1:1, except where the mapping is overridden by further
     equivalence mappings lower down the hierarchy.   This equivalence
     may be achieved in three ways:

     1.   All of the nodes below this point are RFC 822, and the MIXER
          mapping defines the X.400 addresses for these nodes.

     2.   All of the nodes below this point are X.400, and the MIXER
          mapping defines the  RFC 822 addresses for these nodes.

     3.   There are X.400 and RFC 822 nodes below this point, and
          addressing is managed in a manner which  ensures the
          equivalence.   The rules to achieve this are  defined by
          MIXER.

     A set of global mappings to enable a clean transformation between
     the X.400 and RFC 822  namespaces is therefore defined by
     deployment of MIXER.

          When an equivalence point is defined, a systematic mapping
     for the the inferior nodes in the two hierarchies follows.   This
     is a 1:1 the mapping between the nodes in the subtrees.  For
     example, given the the equivalence defined above:

             the domain "R-D.Salford.AC.UK" algorithmically maps with
             C="GB", ADMD="GOLD 400", PRMD="UK.AC", O="Salford", OU="R-D"


     Note that when an equivalence is defined, that this can be re-
     defined for lower points in the hierarchy.   However, it is not
     possible to declare contained subtrees to be un-mappable.

          The equivalence mapping also provides a mechanism to deal    |



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     with missing elements in the X.400 hierarchy (most commonly the
     PRMD).  A domain may be associated with an omitted attribute in
     conjunction with several present ones.  When performing the
     algorithmic insertion of components lower in the hierarchy, the
     omitted value shall be skipped.  For example:

             If the domain HNE.EGM" is mapped  with
             "C=TC", "ADMD=ECQ", "PRMD=HNE", and omitted organization

     then

             "ZI.HNE.EGM" is algorithmically mapped with
             "C=TC", "ADMD=ECQ", "PRMD=HNE", "OU=ZI"

     Attributes may have null values, and  this is treated separately
     from omitted attributes (while it is not ideal
      to make this distinction, it is useful in practice).

     4.2.1.  Directory and Nameserve Mappings                          |

     When the global mapping is supported by X.500 or DNS, there is
     the possibility that results will be indeterminate due to
     timeout.  Lookup should be repeated until a value is determined,
     in order to maintain a correct and consistent global mapping.     |

          Where the mapping relates to addresses in the message        |
     header, there shall be a timeout in the range of 1-4 hours.   If  |
     a mapping cannot be done in this time, address encapsulation      |
     shall be used.

     4.3.  EBNF.822-address <-> MTS.ORAddress

     This section defines the basic address mapping.

     4.3.1.  X.400 encoded in RFC 822

     This section defines how X.400 addresses are represented in RFC
     822 the addresses.

          The std-or-address syntax is  used to encode O/R Address
     information in the 822.local-part of EBNF.822-address.  Where
     there is an applicable equivalence mapping, further  O/R Address
     information is associated with the 822.domain component.  This
     cannot be used in the general case, due to character set



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     problems, and to the variants of X.400 O/R Addresses which use
     different attribute types.  The only way to encode the full
     PrintableString character set in a domain is by use of the
     822.domain-ref syntax (i.e. 822.atom).  This is likely to cause
     problems on many systems.  The effective character set of domains
     is in practice reduced from the RFC 822 set, by restrictions
     imposed by domain conventions and policy [10], and by the BNF     |
     definition in SMTP.

          A generic 822.address consists of a 822.local-part and a
     sequence of 822.domains (e.g., <@domain1,@domain2:user@domain3>).
     All except the 822.domain associated with the 822.local-part
     (domain3 in this case) are considered to specify routing within
     the RFC 822 world, and will not be interpreted by the gateway
     (although they may have identified the gateway from within the
     RFC 822 world).

          The  822.domain associated with the 822.local-part
     identifies the gateway from within the RFC 822 world.  This final
     822.domain may be used to determine some number of O/R Address
     attributes, where this does not conflict with the first role.
     RFC 822 routing to gateways will usually be set up to facilitate
     the 822.domain being used for both purposes.

          In the case that there is no applicable equivalence mapping,
     all of the X.400 address is encoded in the 822.local-part and the |
     the 822.domain identifies the gateway to which the message is
     being sent.  This technique may be used by the RFC 822 user for   |
     any X.400 address where the equivalence mapping is not known.

          In the case that there is an applicable equivalence mapping,
     the the maximum number of attributes are encoded in the
     822.domain.  The remaining attributes are encoded on the LHS,
     using the EBNF.std-or-address syntax.  For example:

             /I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM

     encodes the MTS.ORAddress consisting of:









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             MTS.CountryName                       = "TC"
             MTS.AdministrationDomainName          = "BTT"
             MTS.OrganizationName                  = "Widget"
             MTS.OrganizationalUnitNames.value     = "Marketing"
             MTS.PersonalName.surname              = "Linnimouth"
             MTS.PersonalName.initials             = "J"
             MTS.PersonalName.generation-qualifier = "5"

     on the basis of an equivalence between:

             Domain: Widget.COM
             O/R Address: C="TC", ADMD="BTT", O="Widget"

     Given the O/R address, the domain Widget.COM is determined from
     the the equivalence mapping and the next component is determined
     algorithmically to give Marketing.Widget.COM.  The remaining
     attributes are encoded on the LHS in 822.local-part.

          There is a further mechanism to simplify the encoding of
     common cases, where the only attributes to be encoded on the LHS  |
     are (non-Teletex) Personal Name attributes which comply with the
     restrictions of 4.2.1.  To achieve this, the 822.local-part shall
     be encoded as EBNF.encoded-pn.  In the previous example, if the
     GenerationQualifier was not present in the O/R Address, it would
     map with the RFC 822 address:  J.Linnimouth@Marketing.Widget.COM.

          From the standpoint of the RFC 822 Message Transfer System,
     the domain specification is used to route the message in the
     standard manner.  The standard domain mechanisms are used to
     select appropriate gateways for the corresponding O/R Address
     space.  It is the responsibility of the management that defines
     the equivalence mapping to define routing in a the manner which
     will enable the message to be delivered.

     4.3.2.  RFC 822 encoded in X.400

     The previous section showed a mapping from X.400 to RFC 822.  In
     the case where  the mapping was symmetrical and based on the the
     equivalence mapping, this has also shown how RFC 822 is encoded
     in the X.400.   This equivalence cannot be used for all RFC 822
     addresses.

          The general case is mapped by use of domain defined



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     attributes.  A Domain defined type "RFC-822" is defined. The
     associated attribute value is an ASCII string encoded according
     to Section 3.3.3 of this specification. The interpretation of the
     ASCII string follows RFC 822, and RFC 1123 [10,16].  Domains
     shall always be fully qualified.

          Other O/R Address attributes will be used to identify a
     context in which the O/R Address will be interpreted.  This might
     be a Management Domain, or some part of a Management Domain which
     identifies a gateway MTA.  For example:

             C               = "GB"
             ADMD            = "GOLD 400"
             PRMD            = "UK.AC"
             O               = "UCL"
             OU              = "CS"
             "RFC-822"      =  "Jimmy(a)WIDGET-LABS.CO.UK"

     OR

             C               = "TC"
             ADMD            = "Wizz.mail"
             PRMD            = "42"
             "rfc-822"       = "postel(a)venera.isi.edu"

     Note in each case the PrintableString encoding of "@" as "(a)".
     In the second example, the "RFC-822" domain defined attribute is
     interpreted everywhere within the (Private) Management Domain.
     In the first example, further attributes are needed within the
     Management Domain to identify a gateway.  Thus, this scheme can
     be used with varying levels of Management Domain co-operation.

          There is a limit of 128 characters in the length of value of
     a domain defined attribute, and an O/R Address can have a
     maxmimum of four domain defined attributes.  Where the printable
     string generated from the RFC 822 address exceeds this value,
     additional domain defined attributes are used to enable up to 512
     characters to be encoded.  These attributes shall be filled
     completely before the next one is started.   The DDA keywords
     are:  RFC822C1; RFC822C2; RFC822C3.  Longer addresses cannot be
     encoded.

          There is, analogous with 4.3.1, a means to associate parts
     of the O/R Address hierarchy with domains.  There is an analogous



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     global mapping, which in most cases will be the inverse of the
     domain to O/R address mapping.  The mapping is maintained
     separately, as there may be differences (e.g., two alternate
     domain names map to the same set of O/R address components).

     4.3.3.  Component Ordering

     In most cases, ordering of O/R Address components is not
     significant for the mappings specified.  However, Organizational
     Units (printable string and teletex forms) and Domain Defined
     Attributes are specified as SEQUENCE in MTS.ORAddress, and so
     their order may be significant.  This specification needs to take
     account of this:

     1.   To allow consistent mapping into the domain hierarchy

     2.   To ensure preservation of order over multiple mappings.

     There are three places where an order is specified:

     1.   The text encoding (std-or-address) of MTS.ORAddress as used
          in the local-part of an RFC 822 address.  An order is needed
          for those components which may have multiple values
          (Organizational Unit, and Domain Defined Attributes). When
          generating an 822.std-or-address, components of a given type
          shall be in hierarchical order with the most significant
          component on the RHS.  If there is an Organization
          Attribute, it shall be to the right of any Organizational
          Unit attributes.  These requirements are for the following
          reasons:

     -         Alignment to the hierarchy of other components in RFC
               822 addresses (thus, Organizational Units will appear
               in the same order, whether encoded on the RHS or LHS).  |

     -         Backwards compatibility with RFC 987/1026.

     -         To ensure that gateways generate consistent addresses.
               This is both to help end users, and to generate
               identical message ids.

          Further, it is recommended that all other attributes are
          generated according to this ordering, so that all attributes
          so encoded follow a consistent hierarchy.   When generating



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          822.msg-id, this order shall be followed.

     2.   For the Organizational Units (OU) in MTS.ORAddress, the
          first OU in the SEQUENCE is the most significant, as
          specified in X.400.

     3.   For the Domain Defined Attributes in MTS.ORAddress, the
          First Domain Defined Attribute in the SEQUENCE is the most
          significant.

          Note that although this ordering is mandatory for this
          mapping, there are NO implications on ordering significance
          within X.400, where this is a Management Domain issue.

     4.3.4.  RFC 822 -> X.400 Basic Address Mapping

     There are two basic cases:

     1.   X.400 addresses encoded in RFC 822.  This will also include
          RFC 822 addresses which are given reversible encodings.

     2.   "Genuine" RFC 822 addresses.

     The mapping shall proceed as follows, by first assuming case 1).

     STAGE I.

     1.   If the 822-address is not of the form:

                  local-part "@" domain

          take the domain which will be routed on and apply step 2 of
          stage 1 to derive (a possibly null) set of attributes. Then
          go to stage II.

          NOTE:It may be appropriate to reduce a source route address
               to this form by removal of all bar the last domain.  In
               terms of the design intentions of RFC 822, this would   |
               be an incorrect action. (Note that a an address of the  |
               form local%part@domain is not a source route).
               However, in most real cases, it will do the "right"
               thing and provide a better service to the end user.
               This is a reflection on the excessive and inappropriate
               use of source routing in RFC 822 based systems, despite



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               the discussion in the Host Requirements [10].  Either
               approach, or the intermediate approach of stripping
               only domain references which reference the local
               gateway are conformant to this specification.

     2.   Attempt to parse EBNF.domain as:



                  *( domain-syntax "." ) known-domain


          Where EBNF.known-domain is the longest possible match in the
          set of globally defined mappings described in Section 4.2.
          EBNF.domain-syntax is the restricted domain syntax defined
          in Section 4.2, to which all of the domain components must
          conform for the parse to be successful.  If this fails, and
          the EBNF.domain does not explicitly identify the local
          gateway, go to stage II.  Otherwise no gateway is explicitly |
          identified and all of the information is used by the local
          gateway.  In this case allocate the attributes associated
          with EBNF.known-domain.  For each component, systematically
          allocate the attribute implied by each EBNF.domain-syntax
          component in the order:  C, ADMD, PRMD, O, OU.  Note that if
          the mapping used identifies an "omitted attribute", then
          this attribute should be omitted in the systematic
          allocation.  If this new component exceed an upper bound
          (ADMD: 16; PRMD: 16; O: 64; OU:  32) or it would lead to
          more than four OUs, then go to stage II with the attributes
          derived.

          At this stage, a set of attributes has been derived, which
          will give appropriate routing within X.400.  If any of the
          later steps of Stage I force use of Stage II, then these
          attributes should be used in Stage II.                       |

     3.   If the 822.local-part uses the 822.quoted-string encoding,
          remove this quoting.  If this unquoted 822.local-part has
          leading space, trailing space, or two adjacent spaces go to
          stage II.

     4.   If the unquoted 822.local-part contains any characters not
          in PrintableString, go to stage II.




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     5.   Parse the (unquoted) 822.local-part according to the EBNF
          EBNF.std-or-address.  Checking of upper bounds should not be
          done at this point.  If this parse fails, parse the local-
          part according to the EBNF EBNF.encoded-pn.  If this parse
          fails, go to stage II.  The result is a set of type/value
          pairs.  If the set of attributes leads to an address of any
          form other than mnemonic form, then only these attributes
          should be taken. If (for mnemonic form) the values generated
          conflict with those derived in step 2 (e.g., a duplicated
          country attribute), the domain is assumed to be a remote
          gateway.  In this case, take only the LHS derived
          attributes, together with any RHS derived attributes which
          are more significant than the most significant attribute
          which is duplicated (e.g., if there is a duplicate PRMD, but
          no LHS derived ADMD and country, then the ADMD and country
          should be taken from the RHS).  Otherwise add LHS and RHS
          derived attributes together.

     6.   Associate the EBNF.attribute-value syntax (determined from
          the identified type) with each value, and check that it
          conforms.  If not, go to stage II.

     7.   Ensure that the set of attributes conforms both to the
          MTS.ORAddress specification and to the restrictions on this
          set given in X.400, and that no upper bounds are exceeded
          for any attribute.  If not go to stage II.

     8.   Build the O/R Address from this information.


     STAGE II.

     This will only be reached if the RFC 822 EBNF.822-address is not
     a valid X.400 encoding.  This implies that the address must refer
     to a recipient on an RFC 822 system.  Such addresses shall be
     encoded in an X.400 O/R Address using a domain defined attribute.

     1.   Convert the EBNF.822-address to PrintableString, as
          specified in Chapter 3.

     2.   Generate the "RFC-822" domain defined attribute  from this
          string.

     3.   Build the rest of the O/R Address in the manner described



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          below.

     It may not be possible to encode the domain defined attribute due
     to length restrictions.  If the limit is exceeded by a mapping at
     the MTS level, then the gateway shall reject the message in
     question.  If this occurs at the IPMS level, then the action will
     depend on the policy being taken for IPMS encoding, which is
     discussed in Section 5.1.3.

     If Stage I has identified a set of attributes, use these to build
     the remainder of the address.  The administrative equivalence of
     the mappings will ensure correct routing through X.400 to a
     gateway back to RFC 822.

          If Stage I has not identified a set of attributes, the
     remainder of the O/R address effectively identifies a source
     route to a gateway from the X.400 side.  There are three cases,
     which are handled differently:                                    |

     SMTP Return Address                                               |
          This shall be set up so that errors are returned through the
          same gateway.  Therefore, the O/R Address of the local
          gateway shall be used.

     IPMS Addresses
          These are optimised for replying.  In general, the message
          may end up anywhere within the X.400 world, and so this
          optimisation identifies a gateway appropriate for  the RFC
          822 address being converted.  The 822.domain to which the
          address would be routed is used to select an appropriate
          gateway. A globally defined set of mappings is used, which
          identifies (the O/R Address components of) appropriate
          gateways for parts of the domain namespace.  The longest
          possible match on the 822.domain defines which gateway to
          use, according to the equivalence mappings defined in
          Section 4.2.

          This global mapping is used for parts of the RFC 822
          namespace which do not have an administrative equivalence
          with any part of the X.400 namespace, but for which it is
          desirable to identify a preferred X.400 gateway in order to
          optimise routing.

          If no mapping is found for the 822.domain, a default value



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          (typically that of the local gateway) is used.  It is never
          appropriate to ignore the globally defined mappings.  In
          some cases, it may be appropriate to locally override the
          globally defined mappings (e.g., to identify a gateway close
          to a recipient of the message).  This is likely to be where
          the global mapping identifies a public gateway, and the
          local gateway has an agreement with a private gateway which
          it prefers to use.                                           |

     SMTP Recipient                                                    |
          As the RFC 822 and X.400 worlds are in principle fully
          connected, there should be no technical reason for this
          situation to occur. In practice, this is not the case.  In   |
          some cases, routing may be configured to use X.400 to        |
          connect an RFC 822 island to the Internet.  The information
          that this part of the domain space should be routed by X.400
          rather than remaining within the RFC 822 world will be
          configured privately into the gateway in question.  The O/R
          address shall then be generated in the same manner as for an
          IPMS address, using the globally defined mappings. It is to
          support this case that the definition of the global domain
          to gateway mapping is important, as the use of this mapping
          will lead to a remote X.400 address, which can be routed by
          X.400 routing procedures.  The information in this mapping
          shall not be used as a basis for deciding to convert a
          message from RFC 822 to X.400.

     Two examples are given:

     Example 1: (Address not in "localpart" "@" "domainpart")

     @relay.co.uk:userb@host2
         maps to
     c=gb; a= ; p=uk.ac; o=mhs-relay; dd.rfc-822=(a)relay.co.uk:userb(a)host2;

     Example 2: (Address with non printablestring characters)

     Tom_Harris@cs.widget.com
          maps to
     c=us; a=MCI; P=relay; dd.rfc-822=Tom(u)Harris(a)cs.widget.com;







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     4.3.4.1.  Heuristics for mapping RFC 822 to X.400

     The following heuristic, which  relates to ordering of address    |
     components, may be used when mapping from RFC 822 to X.400.  The
     ordering of attributes may be inverted or mixed.  For this
     reason, the following heuristics may be applied:

     6.   If there is an Organization attribute to the left of any Org
          Unit attribute, assume that the hierarchy is inverted.  This
          is to facilitate the situation where a user has input the
          attributes in reverse hierarchical order.  To do this the
          gateway shall first map according to the order defined in
          4.3.3.    If this mapping generates an address which X.400
          address verification shows to be invalid, this heuristic may
          be applied as an alternative to immediate rejection of the
          address.

     4.3.5.  X.400 -> RFC 822 Basic Address Mapping


     There are two basic cases:

     1.   RFC 822 addresses encoded in X.400.

     2.   "Genuine" X.400 addresses.  This may include symmetrically
          encoded RFC 822 addresses.

     When a MTS Recipient O/R Address is interpreted, gatewaying will
     be selected if there is a single "RFC-822" domain defined         |
     attribute present.  In this case, use mapping A and in other      |
     cases, use mapping B.                                             |

          RFC 1327 specified that this should only be done when the    |
     gateway identfied is local or otherwise known, and identified the |
     approach specified here as a pragmatic option.  Experience has    |
     shown that this is effective in practice, despite theoretical     |
     problems.                                                         |

          If a gateway wishes to make a mapping in a manner similar to |
     RFC 1327, but does not wish for this global interpretation (e.g., |
     to support an RFC 822 local systems, which does not use global    |
     addressing), then it should choose a private domain defined       |
     attribute, different to "RFC-822".  An RFC 1327 gateway might be  |
     configurable to operate in this manner.



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     Mapping A                                                         *

     1.   Map the domain defined attribute value to ASCII, as defined
          in Chapter 3, and drop all other attributes.

     Mapping B.

     This is used for X.400 addresses which do not use the explicit
     RFC 822 encoding.

     1.   For all string encoded attributes, remove any leading or
          trailing spaces, and replace adjacent spaces with a single
          space.

          The only attribute which is permitted to have zero length is
          the ADMD.  This should be mapped onto a single space.

          These transformations are for lookup only.   If an
          EBNF.std-or-address mapping is used as in 4), then the
          original values should be used.

     2.   Map numeric country codes to the two letter values (as       |
          defined in ISO 3166).

     3.   Noting the hierarchy specified in 4.3.1 and including
          omitted attributes, determine the maximum set of attributes
          which have an associated domain specification in the
          globally defined mapping.  If no match is found, allocate    |
          the domain as described below, and go to step 5. The default |
          domain to be used is the specification of the local gateway. |
          A gateway may use other domains according to private mapping |
          tables or heuristics.   For example, it may choose a domain  |
          which it knows to provide a free gateway service to the      |
          mapped address.

          In cases where the address refers to an X.400 UA, it is
          important that the generated domain will correctly route to
          a gateway.  In general, this is achieved by carefully co-
          ordinating RFC 822 routing with the definition of the global
          mappings, as there is no easy way for the gateway to make
          this check.  One rule that shall be used is that domains
          with only one component will not route to a gateway.  If the
          generated domain does not route correctly, the address is
          treated as if no match is found.



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     4.   The mapping identified  in 3) gives a domain, and an O/R
          address prefix.  Follow the hierarchy: C, ADMD, PRMD, O, OU.
          For each successive component below the O/R address prefix,
          which conforms to the syntax EBNF.domain-syntax (as defined
          in 4.3.1), allocate the next subdomain.  At least one
          attribute of the X.400 address shall not be mapped onto
          subdomain, as 822.local-part cannot be null.  If there are
          omitted attributes in the O/R address prefix, these will
          have correctly and uniquely mapped to a domain component.
          Where there is an attribute omitted below the prefix, all
          attributes remaining in the O/R address shall be encoded on
          the LHS.  This is to ensure a reversible mapping. For
          example, if there is an address /S=XX/O=YY/ADMD=A/C=NN/ and
          a mapping for /ADMD=A/C=NN/ is used, then /S=XX/O=YY/ is
          encoded on the LHS.

     5.   If the address contains any attribute not used in mnemonic
          form, then all of the attributes in the address should be
          encoded on the LHS in EBNF.std-or-address syntax, as
          described below.

          For addresses of mnemonic form, if the remaining components
          are personal-name components, conforming to the restrictions
          of 4.2.1, then EBNF.encoded-pn is derived to form
          822.local-part.  In other cases the remaining components are
          simply encoded as 822.local-part using the
          EBNF.std-or-address syntax.  If necessary, the
          822.quoted-string encoding is used.  The following are
          examples of legal quoting: "a b".c@x; "a b.c"@x.  Either
          form may be generated, but the latter is preferred.

          If the derived 822.local-part can only be encoded by use of
          822.quoted-string, then use of the mapping defined in[19]
          may be appropriate.  Use of this mapping is discouraged.     |

     Editor's Note:                                                    |
          Can we remove the previous paragraph?

     Three examples are given.                                         |

     Editor's Note:                                                    |
          I have had a lot of comments on the inaccuracy of these      |
          examples.  Are they worth retaining?  If so, can they be     |
          carefully verified.



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     Example 1: (Address with missing X.400 elements and no specific
     mapping rule for "o=sales; a=Master400; C=it", where a mapping    |
     exsits for master400.it)

     C=it; A=Master400; O=sales; S=Support;                             |
         maps to
     /S=Support/o=sales/@Master400.it                                   |


     Example 2: (Address with illegal characters in RFC822 generated
     domain if default hierarchical translation (specific mapping rule
     is existing for c=fr; a=atlas; p=autoroutes) is used)

     C=fr; A=atlas; P=autoroutes; O=Region Parisienne; S=rensignments;  |
         maps to
     "/S=rensignments/o=Region Parisienne/"@autoroutes.fr               |

     Example 3:  (Address containing elements not mappable into RFC822
     local part)

     C=it; A=PtPostel; DDA.cap=20100; DDA.ph1=Via Maggiore 11; DDAs.city=Milano; S=Rossi;|
         MAPS TO
     "/DD.Cap=20100/DD.ph1=Via Maggiore 11/DD.City=Milano/S=Rossi/"@ptpostel.it|


     4.4.  Repeated Mappings

     There are two types of repeated mapping:

     1.   A recursive mapping, where the repeat is within one gateway

     2    A source route, where the repetition occurs across multiple
          gateways

     4.4.1.  Recursive Mappings

     It is possible to supply an address which is recursive at a
     single gateway.  For example:

             C          = "XX"
             ADMD       = "YY"
             O          = "ZZ"
             "RFC-822"  = "Smith(a)ZZ.YY.XX"




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     This is mapped first to an RFC 822 address, and then back to the
     X.400 address:

             C          = "XX"
             ADMD       = "YY"
             O          = "ZZ"
             Surname    = "Smith"

     In some situations this type of recursion may be frequent.  It is
     important where this occurs, that no unnecessary protocol         |
     conversion occurs. This will minimise loss of service.

     4.4.2.  Source Routes

     The mappings defined are symmetrical and reversible across a
     single gateway.  The symmetry is particularly useful in cases of
     (mail exploder type) distribution list expansion.  For example,
     an X.400 user sends to a list on an RFC 822 system which he
     belongs to.  The received message will have the originator and
     any 3rd party X.400 O/R Addresses in correct format (rather than
     doubly encoded).  In cases (X.400 or RFC 822) where there is
     common agreement on gateway identification, then this will apply
     to multiple gateways.

          When a message traverses multiple gateways, the mapping will
     always be reversible, in that a reply can be generated which will
     correctly reverse the path.  In many cases, the mapping will also
     be symmetrical, which will appear clean to the end user.  For
     example, if countries "AB" and "XY" have RFC 822 networks, but
     are interconnected by X.400, the following may happen:  The
     originator specifies:

             Joe.Soap@Widget.PTT.XY

     This is routed to a gateway, which generates:

             C               = "XY"
             ADMD            = "PTT"
             PRMD            = "Griddle MHS Providers"
             Organization    = "Widget Corporation"
             Surname         = "Soap"
             Given Name      = "Joe"

     This is then routed to another gateway where the mapping is



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     reversed to give:

             Joe.Soap@Widget.PTT.XY

     Here, use of the gateway is transparent.

          Mappings will only be symmetrical where mapping equivalences |
     are defined. In other cases, the reversibility is more important,
     due to the (far too frequent) cases where RFC 822 and X.400
     services are partitioned.

          The syntax may be used to source route.  THIS IS STRONGLY
     DISCOURAGED.  For example:

             X.400 -> RFC 822  -> X.400

             C             = "UK"
             ADMD          = "Gold 400"
             PRMD          = "UK.AC"
             "RFC-822"     = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"

     This will be sent to an arbitrary UK Academic Community gateway
     by X.400.  Then it will be sent by JNT Mail to another gateway
     determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria).  This
     will then derive the X.400 O/R Address:

             C             = "FR"
             ADMD          = "ATLAS"
             PRMD          = "Inria"
             PN.S          = "Duval"
             "Title"       = "Manager"

     Similarly:
     RFC 822 -> X.400 -> RFC 822

     "/RFC-822=jj(a)seismo.css.gov/PRMD=AC/ADMD=BT/C=GB/"@monet.berkeley.edu

     This will be sent to monet.berkeley.edu by RFC 822, then to the
     AC PRMD by X.400, and then to jj@seismo.css.gov by RFC 822.

     4.5.  Directory Names

     Directory Names are an optional part of O/R Name, along with O/R
     Address.  The RFC 822 addresses are mapped onto the O/R Address



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     component. As there is no functional mapping for the Directory
     Name on the RFC 822 side, a textual mapping is used.  There is no
     requirement for reversibility in terms of the goals of this
     specification.  There may be some loss of functionality in terms
     of third party recipients where only a directory name is given,
     but this seems preferable to the significant extra complexity of
     adding a full mapping for Directory Names.

          The Directory Name shall be represented within an RFC 822
     comment.  Any reasonable format for representing the directory
     name may be used.  It is recommended that the directory string
     format of RFC 1485 is used [25].  The User Friendly Name form of
     RFC 1484 may also be used [26].

     4.6.  MTS Mappings

     The basic mappings at the MTS level are:

     1) SMTP originator ->                                              |
                   MTS.PerMessageSubmissionFields.originator-name
        MTS.OtherMessageDeliveryFields.originator-name ->
                   SMTP originator                                      |

     2) SMTP recipient ->                                               |
                   MTS.PerRecipientMessageSubmissionFields
        MTS.OtherMessageDeliveryFields.this-recipient-name ->
                   SMTP recipient                                       |

     SMTP recipients and return addresses are encoded as               |
     EBNF.822-address.

          The MTS Originator is always encoded as MTS.OriginatorName,
     which maps onto MTS.ORAddressAndOptionalDirectoryName, which in
     turn maps onto MTS.ORName.

     4.6.1.  RFC 822 -> X.400 MTS Mappings

     From the SMTP Originator, use the basic ORAddress mapping, to     |
     generate MTS.PerMessageSubmissionFields.originator-name
     (MTS.ORName), without a DirectoryName.

          For recipients, the following settings are made for each
     component of MTS.PerRecipientMessageSubmissionFields.




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     recipient-name
          This is derived from the SMTP recipient by the basic         |
          ORAddress mapping.

     originator-report-request
          This is be set according to content return policy, as
          discussed in Section 5.2.

     explicit-conversion
          This optional component is omitted, as this service is not
          needed

     extensions
          The default value (no extensions) is used

     4.6.2.  X.400 -> RFC 822 MTS Mappings

     The basic functionality is to generate the SMTP originator and    |
     recipients.  There is information present on the X.400 side,
     which cannot be mapped into analogous SMTP services.  For this    |
     reason, new RFC 822 fields are added for the MTS Originator and
     Recipients.  The information discarded at the SMTP level will be  |
     present in these fields. In some cases a (positive) delivery
     report will be generated.

     4.6.2.1.  SMTP Mappings                                           |

     Use the basic ORAddress mapping, to generate the SMTP originator  |
     (return address) from
     MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName).  If
     MTS.ORName.directory-name is present, it is discarded.  (Note
     that it will be presented to the user, as described in 4.6.2.2).

          The mapping  uses the MTA level information, and maps each   |
     value of MTA.PerRecipientMessageTransferFields.recipient-name,    |
     where the responsibility bit is set, onto an SMTP recipient.      |

     Note:The SMTP recipient is conceptually generated from
          MTS.OtherMessageDeliveryFields.this-recipient-name.  This is
          done by taking
          MTS.OtherMessageDeliveryFields.this-recipient-name, and      |
          generating an SMTP recipient according to the basic          |
          ORAddress mapping, discarding MTS.ORName.directory-name if
          present.  However, if this model was followed exactly, there



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          would be no possibility to have multiple SMTP recipients on  |
          a single message.  This is unacceptable, and so layering is
          violated.                                                    *

     4.6.2.2.  Generation of RFC 822 Headers

     Not all per-recipient information can be passed at the SMTP       |
     level.  For this reason, two new RFC 822 headers are created, in
     order to carry this information to the RFC 822 recipient.  These
     fields are "X400-Originator:"  and "X400-Recipients:".

          The "X400-Originator:" field is set to the same value as the |
     SMTP originator.  In addition, if
     MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName)
     contains MTS.ORName.directory-name then this Directory Name shall
     be represented in an 822.comment.

          Recipient names, taken from each value of
     MTS.OtherMessageDeliveryFields.this-recipient-name and
     MTS.OtherMessageDeliveryFields.other-recipient-names are made
     available to the RFC 822 user by use of the "X400-Recipients:"
     field.  By taking the recipients at the MTS level, disclosure of
     recipients will be dealt with correctly.  However, this conflicts
     with a desire to optimise mail transfer.  There is no problem
     when disclosure of recipients is allowed. Similarly, there is no
     problem if there is only one RFC 822 recipient, as the
     "X400-Recipients" field is only given one address.

          There is a problem if there are multiple RFC 822 recipients,
     and disclosure of recipients is prohibited.  In this case,        |
     discard the per-recipient information, and insert a field:

             X400-Recipients: non-disclosure:;


     If any MTS.ORName.directory-name is present, it shall be          *
     represented in an 822.comment.

          If
     MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name
     is present, then there has been redirection,  or there has been
     distribution list expansion.  Distribution list expansion is a
     per-message option, and the information associated with this is
     represented by the "DL-Expansion-History:" field described in



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     Section 5.3.6.  Other information is represented in an
     822.comment associated associated with
     MTS.OtherMessageDeliveryFields.this-recipient-name, The message
     may be delivered to different RFC 822 recipients, and so several
     addresses in the "X400-Recipients:" field may have such comments.
     The non-commented recipient is the RFC 822 recipient. The EBNF of
     the comment is:

             redirect-comment  =
                      [ "Originally To:" ] mailbox "Redirected"
                      [ "Again" ] "on" date-time
                      "To:"  redirection-reason

             redirection-reason =
                      "Recipient Assigned Alternate Recipient"
                      / "Originator Requested Alternate Recipient"
                      / "Recipient MD Assigned Alternate Recipient"
                      / "Recipient Directory Substitution Alternate Recipient"

     It is derived from
     MTA.PerRecipientMessageTransferFields.extension.redirection-history.
     An example of this is:

     X400-Recipients: postmaster@widget.com (Originally To:
           sales-manager@sales.widget.com Redirected
           on Thu, 30 May 91 14:39:40 +0100 To: Originator Assigned
           Alternate Recipient postmaster@sales.widget.com Redirected
           Again on Thu, 30 May 91 14:41:20 +0100 To: Recipient MD
           Assigned Alternate Recipient)



          In addition the following per-recipient services from
     MTS.OtherMessageDeliveryFields.extensions are represented in
     comments if they are used.  None of these services can be
     provided on RFC 822 networks, and so in general these will be
     informative strings associated with other MTS recipients. In some
     cases, string values are defined.  For the remainder, the string
     value shall be chosen by the implementor.   If the parameter has
     a default value, then no comment shall be inserted when the
     parameter has that default value.

     requested-delivery-method




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     physical-forwarding-prohibited
          "(Physical Forwarding Prohibited)".

     physical-forwarding-address-request
          "(Physical Forwarding Address Requested)".

     physical-delivery-modes

     registered-mail-type

     recipient-number-for-advice

     physical-rendition-attributes

     physical-delivery-report-request
          "(Physical Delivery Report Requested)".

     proof-of-delivery-request
          "(Proof of Delivery Requested)".

     4.6.2.3.  Delivery Report Generation

     If SMTP is used, the behaviour is specified in Appendix A.  In    |
     other cases, if                                                   |
     MTA.PerRecipientMessageTransferFields.per-recipient-indicators
     requires a positive delivery notification, this shall be
     generated by the gateway.  Supplementary Information shall be set
     to indicate that the report is gateway generated.  This
     information shall include the name of the gateway generating the
     report.

     4.6.3.  Message IDs (MTS)

     A mapping from 822.msg-id to MTS.MTSIdentifier is defined.  The
     reverse mapping is not needed, as MTS.MTSIdentifier is always
     mapped onto new RFC 822 fields.  The value of
     MTS.MTSIdentifier.local-part will facilitate correlation of
     gateway errors.

          To map from 822.msg-id, apply the standard mapping to
     822.msg-id, in order to generate an MTS.ORAddress.  The Country,
     ADMD, and PRMD components of this are used to generate
     MTS.MTSIdentifier.global-domain-identifier.
     MTS.MTSIdentifier.local-identifier is set to the 822.msg-id,



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     including the braces "<" and ">".   If this string is longer than
     MTS.ub-local-id-length (32), then it is truncated to this length.

          The reverse mapping is not used in this specification.  It
     would be applicable where MTS.MTSIdentifier.local-identifier is
     of syntax 822.msg-id, and it algorithmically identifies
     MTS.MTSIdentifier.

     4.7.  IPMS Mappings

     All RFC 822 addresses are assumed to use the 822.mailbox syntax.
     This includes all 822.comments associated with the lexical tokens
     of the 822.mailbox.  In the IPMS O/R Names are encoded as
     MTS.ORName.  This is used within the  IPMS.ORDescriptor,
     IPMS.RecipientSpecifier, and IPMS.IPMIdentifier.  An asymmetrical
     mapping is defined between these components.

     4.7.1.  RFC 822 -> X.400

     To derive IPMS.ORDescriptor from an RFC 822 address.

     1.   Take the address, and extract an EBNF.822-address.  Any      |
          source routing shall be removed.  This can be derived
          trivially from either the 822.addr-spec or 822.route-addr
          syntax.  This is mapped to MTS.ORName as described above,
          and used as IMPS.ORDescriptor.formal-name.

     2.   A string shall be built consisting of (if present):

     -         The 822.phrase component if the 822.address is an
               822.phrase 822.route-addr construct.

     -         Any 822.comments, in order, retaining the parentheses.

          This string is then encoded into T.61 using a human oriented |
          mapping (as described in Section 3.5).  If the string is not
          null, it is assigned to IPMS.ORDescriptor.free-form-name.

     3.   IPMS.ORDescriptor.telephone-number is omitted.

     If IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier,
     IPMS.RecipientSpecifier.reply-request and
     IPMS.RecipientSpecifier.notification-requests are set to default
     values (false and none).



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          If the 822.group construct is present, any included
     822.mailbox is encoded as above to generate a separate
     IPMS.ORDescriptor.  The 822.group is  mapped to T.61 (as
     described in Section 3.5), and a IPMS.ORDescriptor with only an
     free-form-name component built from it.

     4.7.2.  X.400 -> RFC 822

     Mapping from IPMS.ORDescriptor to RFC 822 address.  In the basic
     case, where IPMS.ORDescriptor.formal-name is present, proceed as
     follows.

     1.   Encode IPMS.ORDescriptor.formal-name (MTS.ORName) as
          EBNF.822-address.

     2a.  If IPMS.ORDescriptor.free-form-name is present, convert it
          to ASCII or T.61 (Section 3.5), and use this as the
          822.phrase component of 822.mailbox using the 822.phrase
          822.route-addr construct.

     2b.  If IPMS.ORDescriptor.free-form-name is absent.  If
          EBNF.822-address is parsed as 822.addr-spec use this as the
          encoding of 822.mailbox.  If EBNF.822-address is parsed as   |
          822.route 822.addr-spec, then an 822.phrase taken from
          822.local-part is added.

     3    If IPMS.ORDescriptor.telephone-number is present, this is
          placed in an 822.comment, with the string "Tel ".  The
          normal international form of number is used.  For example:

                  (Tel +44-181-333-7777)


     4.   If IPMS.ORDescriptor.formal-name.directory-name is present,
          then a text representation is placed in a trailing
          822.comment.

     5.   If IPMS.RecipientSpecifier.report-request has any non-
          default values, then an 822.comment "(Receipt Notification
          Requested)", and/or "(Non Receipt Notification Requested)",
          and/or "(IPM Return Requested)" may be appended to the       |
          address. "(Receipt Notification Requested)" may be used to   |
          infer "(Non Receipt Notification Requested)".  The effort of
          correlating P1 and P2 information is too great to justify



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          the gateway sending Receipt Notifications.

          In RFC 1327, inclusion of these comments was mandatory.
          Experience has shown that the clutter and confusion caused
          to RFC 822 users does not justify the information conveyed.
          Implementors are recommended to not include these comments.
          Unless an application is found where retention of these
          comments is desirable, they will be dropped from the next
          version.

     6.   If IPMS.RecipientSpecifier.reply-request is True, an
          822.comment "(Reply requested)"  is appended to the address.

     If IPMS.ORDescriptor.formal-name is absent,
     IPMS.ORDescriptor.free-form-name is converted to ASCII, and used
     as 822.phrase within the RFC 822 822.group syntax.  For example:

             Free Form Name ":" ";"

     Steps 3-6 are then followed.

     4.7.3.  IP Message IDs

     There is a need to map both ways between 822.msg-id and
     IPMS.IPMIdentifier.  This allows for X.400 Receipt Notifications,
     Replies, and Cross References to reference an RFC 822 Message ID,
     which is preferable to a gateway generated ID.  A reversible and
     symmetrical mapping is defined.  This provides fully reversible
     mappings when messages pass multiple times across the X.400/RFC
     822 boundary.

          An important issue with messages identifiers is mapping to
     the exact form, as many systems use these ids as uninterpreted
     keys.  The use of table driven mappings is not always
     symmetrical, particularly in the light of alternative domain
     names, and alternative management domains.  For this reason, a
     purely algorithmic mapping is used.  A mapping which is simpler
     than that for addresses can be used for two reasons:

     -    There is no major requirement to make message IDs "natural"

     -    There is no issue about being able to reply to message IDs.
          (For addresses, creating a return path which works is more
          important than being symmetrical).



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     The mapping works by defining a way in which message IDs
     generated on one side of the gateway can be represented on the
     other side in a systematic manner.  The mapping is defined so
     that the possibility of clashes is is low enough to be treated as
     impossible.

     4.7.3.1.  822.msg-id represented in X.400

     IPMS.IPMIdentifier.user is omitted.  The
     IPMS.IPMIdentifier.user-relative-identifier is set to a printable
     string encoding of the 822.msg-id with the angle braces ("<" and
     ">") removed.  The upper bound on this component is 64.  The
     options for handling this are discussed in Section 5.1.3.

     4.7.3.2.  IPMS.IPMIdentifier represented in RFC 822

     The 822.domain of 822.msg-id is set to the value "MHS". The
     822.local-part of 822.msg-id is constructed as follows.  A string
     is build of syntax EBNF.id-loc from IPMS.IPMIdentifier.

             id-loc ::= [ printablestring ] "*"  [ std-or-address ]

     EBNF.printablestring is the
     IPMS.IPMIdentifier.user-relative-identifier, and EBNF.std-or-
     address being an encoding of the IPMS.IPMIdentifier.user derived
     according to this specification.  822.local-part is derived from
     EBNF.id-loc, if necessary using the 822.quoted-string encoding.
     For example:

     <"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>


     4.7.3.3.  822.msg-id -> IPMS.IPMIdentifier

     If the 822.local-part can be parsed as:

             [ printablestring ] "*"  [ std-or-address ]

     and the 822.domain is "MHS", then this ID was X.400 generated.
     If EBNF.printablestring is present, the value is assigned to
     IPMS.IPMIdentifier.user-relative-identifier.  If
     EBNF.std-or-address is present, the O/R Address components
     derived from it are used to set IPMS.IPMIdentifier.user.




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          Otherwise, this is an RFC 822 generated ID.  In this case,
     set IPMS.IPMIdentifier.user-relative-identifier to a printable
     string encoding of the 822.msg-id without the angle braces.

     4.7.3.4.  IPMS.IPMIdentifier -> 822.msg-id

          If IPMS.IPMIdentifier.user is absent, and
     IPMS.IPMIdentifier.user-relative-identifier mapped to ASCII and
     angle braces added parses as 822.msg-id, then this is an RFC 822
     generated ID.

          Otherwise, the ID is X.400 generated.  Use the
     IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form
     string.  Build the 822.local-part of the 822.msg-id with the
     syntax:

             [ printablestring ] "*"  [ std-or-address ]

     The printablestring is taken from
     IPMS.IPMIdentifier.user-relative-identifier.  Use
     822.quoted-string if necessary.  The 822.msg-id is generated with
     this 822.local-part, and "MHS" as the 822.domain.

     4.7.3.5.  Phrase form

     In "In-Reply-To:" and "References:", the encoding 822.phrase may  |
     be used as an alternative to 822.msg-id.  To map from 822.phrase
     to IPMS.IPMIdentifier, assign
     IPMS.IPMIdentifier.user-relative-identifier to the phrase.  When
     mapping from IPMS.IPMIdentifier for "In-Reply-To:" and
     "References:", if IPMS.IPMIdentifier.user is absent and
     IPMS.IPMIdentifier.user-relative-identifier does not parse as
     822.msg-id, generate an 822.phrase rather than adding the domain
     MHS.

     4.7.3.6.  RFC 987 backwards compatibility

     The mapping defined here is different to that used in RFC 987, as
     the RFC 987 mapping lead to changed message IDs in many cases.
     Fixing the problems is preferable to retaining backwards
     compatibility.  An implementation of this standard is encouraged
     to recognise message IDs generated by RFC 987.  This is not
     required.




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          RFC 987 generated encodings may be recognised as follows.
     When mapping from X.400 to RFC 822, if the
     IPMS.IPMIdentifier.user-relative-identifier is "RFC-822" the id
     is RFC 987 generated. When mapping from RFC 822 to X.400, if the
     822.domain is not "MHS", and the 822.local-part can be parsed as

             [ printablestring ] "*"  [ std-or-address ]

     then it is RFC 987 generated.  In each of these cases, it is
     recommended to follow the RFC 987 rules.





































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     Chapter 5 - Detailed Mappings


     This chapter specifies  detailed mappings for the functions
     outlined in Chapters 1 and 2.  It makes extensive use of the
     notations and mappings defined in Chapters 3 and 4.


     5.1.  RFC 822 -> X.400: Detailed Mappings

     The mapping of RFC 822 and MIME messages to X.400 InterPersonal
     Messages is described in Sections 5.1.1 to 5.1.7.   Mapping of
     NOTARY format delivery status notifications, which are all
     messages of type multipart/report and subtype
     delivery-status-notifications to X.400 delivery reports is
     covered in Section 5.1.8.


     5.1.1.  Basic Approach

     A single IP Message is generated from an RFC 822 message.  The    |
     RFC 822 headers are used to generate the IPMS.Heading.

          Some RFC 822 fields cannot be mapped onto a standard IPM
     Heading field, and so an extended field is defined in Section
     5.1.2.  This is then used for fields which cannot be mapped onto
     existing services.

          The message is submitted to the MTS, and the services
     required can be defined by specifying
     MTS.MessageSubmissionEnvelope.  A few parameters of the MTA
     Abstract service are also specified, which are not in principle
     available to the MTS User.  Use of these services allows RFC 822
     MTA level parameters to be carried in the analogous X.400 service
     elements.  The advantages of this mapping far outweigh the
     layering violation.

     5.1.2.  X.400 Extension Field

     An IPMS Extension is defined:







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             rfc-822-field HEADING-EXTENSION
                     VALUE RFC822FieldList
                     ::= id-rfc-822-field-list


             RFC822FieldList ::= SEQUENCE OF RFC822Field

             RFC822Field ::= IA5String

     The Object Identifier id-rfc-822-field-list is defined in
     Appendix D.

          To encode any RFC 822 Header using this extension, an
     RFC822Field element is built using the 822.field omitting the
     trailing CRLF (e.g., "Fruit-Of-The-Day: Kiwi Fruit"). All fields
     shall be unfolded.  There shall be no space before the ":".  The
     reverse mapping builds the RFC 822 field in a straightforward
     manner.  This RFC822Field is appended to the RFC822FieldList,
     which is added to the IPM Heading as an extension field.

     5.1.3.  Generating the IPM

     The IPM (IPMS Service Request) is generated according to the
     rules of this section. The IPMS.IPM.body is generated from the
     RFC 822 message body in the manner described in Section 5.1.5.

          If no specific 1988 features are used, the IPM generated is
     encoded as content type 2.  Otherwise, it is encoded as content
     type 22.  The latter will always be the case if extension heading
     fields are generated.

          When generating the IPM, the issue of upper bounds are       |
     handled as follows. Truncate fields to the upper bounds specified
     in X.400.  This will prevent problems with UAs which enforce
     upper bounds, but will sometimes discard useful information.
     This approach will cause more problems for some fields than
     others (e.g., truncating an O/R Address component that would be
     used to route a reply would be a more severe problem than
     truncating a Free Form Name).  If the Free Form name is
     truncated, it shall be done so that it does not break RFC 822     |
     comments and RFC 1522 encoding.                                   |

     Note:This approach removes a choice of options given in RFC 1327, |



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          based on operational experience.

          The rest of this section concerns IPMS.IPM.heading
     (IPMS.Heading).  The only mandatory component of IPMS.Heading is
     the IPMS.Heading.this-IPM (IPMS.IPMIdentifier).  A default is
     generated by the gateway.  With the exception of "Received:", the
     values of multiple fields are merged (e.g., If there are two
     "To:" fields, then the mailboxes of both are merged to generate a
     single list which is used in the IPMS.Heading.primary-recipients.
     Information shall be generated from the standard RFC 822 Headers
     as follows:

     Date:
          Ignore (Handled at MTS level)

     Received:
          Ignore (Handled at MTA level)

     Message-Id:
          Mapped to IPMS.Heading.this-IPM.  For these, and all other
          fields containing 822.msg-id the mappings of Chapter 4 are
          used for each 822.msg-id.

     From:
          If Sender: is present, this is mapped to
          IPMS.Heading.authorizing-users.  If not, it is mapped to
          IPMS.Heading.originator.  For this, and other components
          containing addresses, the mappings of Chapter 4 are used for
          each address.

     Sender:
          Mapped to IPMS.Heading.originator.

     Reply-To:
          Mapped to IPMS.Heading.reply-recipients.

     To:  Mapped to IPMS.Heading.primary-recipients

     Cc:  Mapped to IPMS.Heading.copy-recipients.

     Bcc: Mapped to IPMS.Heading.blind-copy-recipients if there is at
          least one BCC:  recipient.  If there are no recipients in
          this field, it should be mapped to a zero length sequence.




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     In-Reply-To:
          If there is one value, it is mapped to
          IPMS.Heading.replied-to-IPM, using the 822.phrase or
          822.msg-id mapping as appropriate.  If there are several
          values, they are mapped to IPMS.Heading.related-IPMs, along
          with any values from a "References:" field.

     References:
          Mapped to IPMS.Heading.related-IPMs.

     Keywords:
          Mapped onto a heading extension.

     Subject:
          Mapped to IPMS.Heading.subject.  The field-body uses the
          human oriented mapping referenced in Section 3.3.4.

     Comments:
          Mapped onto a heading extension.  This is a change from
          1327, which specified to generate an IPMS.BodyPart of type
          IPMS.IA5TextBodyPart with
          IPMS.IA5TextBodyPart.parameters.repertoire set to the
          default (ia5), containing the value of the fields, preceded
          by the string "Comments: " and that this body part shall
          precede the other one. Experience has shown that this
          complexity is not justified.  This text is retained to
          facilitate backwards compatibility.

     Encrypted:
          Mapped onto a heading extension.

     Resent-*
          Mapped onto a heading extension.

          Note that it would be possible to use a ForwardedIPMessage
          for these fields, but the semantics are (arguably) slightly
          different, and it is probably not worth the effort.

     Content-Language:
          This fields is defined in RFC 1766 [8].  Map the first two   |
          characters of each value given onto the IPM Languages        |
          extension. If any comments or values longer than two         |
          characters occur, a header extension shall also be           |
          generated.



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     Other Fields
          In particular X-* fields, and "illegal" fields in common
          usage (e.g., "Fruit-of-the-day:") are mapped onto a heading
          extension, unless covered by another section or appendix of
          this specification.  The same treatment is applied to RFC
          822 fields where the content of the field does not conform
          to RFC 822 (e.g., a Date: field with unparseable syntax).

     The MIME heading are mapped as follows. When performing a reverse |
     mapping from X.400 to MIME, these fields may be treated as a hint
     to help convert the message as well as possible.   Only one value
     for each field shall be present in the MIME message that is thus
     generated.

     MIME-Version:
          Mapped onto a heading extension.

     Content-Transfer-Encoding:
          Mapped onto a heading extension.

     Content-Type
          Mapped onto a heading extension.

     Content-ID
          Mapped onto a heading extension.

     Content-Description
          Mapped onto a heading extension.

     5.1.4.  Generating the IPM Body

     If the header does not contain a 822.MIME-Version field, then
     generate a IPMS.Body with a single IPMS.BodyPart of type
     IPMS.IA5TextBodyPart with
     IPMS.IA5TextBodyPart.parameters.repertoire set to the default
     (ia5) containing the body of the RFC 822 message.

          If 822.MIME-Version is present, then the body part is
     analysed as a MIME message and the elements treated as described
     below.

     5.1.4.1.  Mapping Multiparts

     A MIME multipart is a set of content-types and not a message with



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     a set of content types. When the multipart is at the outermost
     MIME header and is either multipart/digest or multipart/mixed,
     elements of the multipart are mapped directly onto IPMS.BodyPart.
     In other cases, a MIME multipart is  mapped to an
     IPMS.MessageBodyPart containing an IPMS.BodyPart for each element
     of the multipart.

          When a nested IPMS.Message is generated from a multipart, an
     IPMS.heading shall always be generated.  The only mandatory field
     is the IPMS.Heading.this-IPM message id, which shall be generated
     by the gateway.  An IPMS.Heading.subject field shall also be
     generated, in order to provide useful information to non-MIME
     capable X.400(88) UAs and to all X.400(84) UAs.  The subject
     field is set as follows according to the multipart subtype:

             mixed:          "Multipart Message"
             alternative:    "Alternative Body Parts containing the same information"
             digest:         "Message Digest"
             parallel:       "Body Parts interpreted in parallel"
             other:          "Multipart Message (<subtype>)"

     For other types of multipart, the multipart subtype shall be
     included in the subject line.

     For each multipart, the following IPMS.HeadingExtension shall be
     generated, with the enumerated value set according to the
     subtype:

             multipart-message HEADING-EXTENSION
                     VALUE MultipartType
                     ::= id-hex-multipart-message

             MultipartType ::= IA5String

     The MultipartType contains the subtype, for example "digest".  If
     this heading is present when mapping from X.400 to MIME, the the
     appropriate multipart may be generated.

     5.1.4.2.  Mapping Content Type Message

     When a message subtype is contained within a MIME message, it is
     mapped to an IPMS.MessageBodyPart according to this
     specification.  Any mappings that would have been made to the MTS
     Abstract Service are placed in



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     IPMS.MessageBodyPart.parameters.delivery-envelope.

          Content type message has three subtypes, which are handled
     as follows:

     message/rfc822
          Mapped onto IPMS.ForwardedIPMessage.

     message/external
          This points to an external body part.  As this will not in
          general be accessible to the X.400 recipient, the body part
          shall be resolved at the gateway, unless it is already       |
          included in a multipart/alternative or the recipient UA is   |
          known to be capable of handling a message/external tunnelled |
          body part.  The gateway shall obtain the body part and then  |
          map it as if it had been included.   If the expiration date
          of the external body part has expired, the gateway may       |
          tunnel the body part.                                        |

     Editor's Note:                                                    |
          There has been comment that this dereference should be made  |
          more optional or the text changed in some way.  Input is     |
          solicited.

     message/partial
          The following heading extension is added, derived from the
          message/partial parameters, in order to facilitate MIME
          capable X.400 UAs to handle messages of this type:

                  partial-message HEADING-EXTENSION
                          VALUE PartialMessage
                          ::= id-hex-partial-message

                  PartialMessage ::=
                          SEQUENCE {
                                  number  INTEGER,
                                  total   INTEGER,
                                  id      IA5String
                                  }


     message/other
          No specific treatment is defined for other subtypes of
          message.  Treatment for new message subtypes may be defined



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          in future versions of MIXER.

     5.1.4.3.  Mapping Other Content Types

     All other MIME content types are atomic data, and can be regarded
     as message attachments.

          The following basic types and some subtypes are defined in
     MIME: text; application; image; audio; video.  The mapping to
     X.400 of the types defined in MIME is specified in RFC 1494bis.

     5.1.4.4.  Mapping to Body Part 15

     RFC 1494bis defines mappings onto Body Part 15.  Similar          |
     considerations apply to body parts 1-14.   MIME defines  fields   |
     which add information to MIME contents.  Two of these are         |
     "Content-ID", and "Content-Description".   When mapping to body
     part 15, this information must be discarded, unless the specific
     body part 15 mapping allows it to be retained.

     5.1.4.5.  Mapping to the EMA FTBP

     EMA has defined a profile for use of the File Transfer Body Part
     (FTBP) .  [28] MIXER spepcifies mapping to FTBP, as defined by    |
     this profile.  MIXER does not define when this mapping is to be   |
     used.  This is a matter for gateway configuration and the user    |
     agent capabilities.

          The exact mapping will depend on the attachment being
     mapped, and so cannot be defined here.  The MIME headers are
     mapped as follows:

     Content-ID:
          If this is present, create an element
          FTBP.FileTransferParameters.related-stored-file.             |
          file-identifier.cross-refernce.message-reference
          FTBP.FileTransferParameters.related-stored-file.             |
          file-identifier.cross-refernce.message-reference and set it
          to the IPM.MessageIdentifier derived from the "Content-ID:".
          FTBP.FileTransferParameters.related-stored-file.
          relationship.descriptive-relationship is set to the string
          "Internet MIME Body Part".
          FTBP.FileTransferParameters.related-stored-file.             |
          file-identifier.cross-refernce.application-crossreference is



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          set to a null OCTET STRING.

     Content-Descriptor:
          This is mapped to the first string in
          FTBP.FileTransferParameters.environment.user-visible-string. |

     A specific mapping for multipart/appledouble is defined.   Noting |
     that the fileTransferData component of an FTBP is a SEQUENCE of   |
     EXTERNAL, the file data component of the multipart is mapped onto |
     the first of two elements of the SEQUENCE, and the                |
     application/applefile component (the finder and resource info) is |
     mapped onto the second element of the sequence.  Applications     |
     which don't care about the finder and resource info can,          |
     therefore, simply ignore the second element and extract the data  |
     from the first element.  The direct reference component of the    |
     first element is set to reflect the original type/subtype of the  |
     MIME data component, according the OID's defined in RFC1494bis.   |

     Editor's Note:                                                    |
          This specification is clearly useful and needed.  Does it    |
          belong in MIXER?   Comments solicited.

     5.1.4.6.  Encapsulation in X.400

     Where no mapping is possible, the gateway may choose to discard
     the body part or to reject the message.  This will depend on
     gateway policy, and configuration knowledge.  Another option is
     to "tunnel" the body part, by encapsulating it in X.400.   This
     section defines an extended body part, based on body part 15,
     which may be used to hold any MIME content.

















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     mime-body-part EXTENDED-BODY-PART-TYPE
           PARAMETERS MimeParameters
                    IDENTIFIED BY id-mime-body-part-parameters
           DATA            OCTET STRING
           ::= id-mime-body-part

     MimeParameters ::=
          SEQUENCE {
                      content-type       IA5String,
                      content-parameters SEQUENCE OF
                                         SEQUENCE {
                                             parameter          IA5String,
                                             parameter-value    IA5String
                                         }
                      other-header-fields RFC822FieldList
                  }

     The OBJECT IDENTIFIERS id-mime-body-part and                      |
     id-mime-body-part-parameters are defined in Appendix D.  A MIME
     content is mapped onto this body part.  The MIME headers of the
     body part are mapped as follows:

     Content-Type:
          The "type/subtype" string is mapped to
          MimeParameters.content-type.

          For each "parameter=value" string create a
          MimeParameters.content-parameters element. The
          MimeParameters.content-Parameters.parameter field is set to
          the parameter and the
          MimeParameters.content-parameters.parameter-value field is
          set to the value.

     OtherTake all other headers and create
          MimeParameters.other-header-fields, by concatenating them
          together.

     Convert the MIME body part into its canonical form, as specified
     in Appendix H of MIME [9].  This canonical form is used to
     generate the mime-body-part.data octet string.

          The Parameter mapping may be used independently of the body
     part mapping (e.g., in order to use a different encoding for a    |



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     mapped MIME body part).

          This body part contains all of the MIME information, and so
     can be mapped back to MIME without loss of information.

     5.1.5.  Mappings to the MTS Abstract Service

     The MTS.MessageSubmissionEnvelope comprises
     MTS.PerMessageSubmissionFields, and
     MTS.PerRecipientMessageSubmissionFields.  The mandatory
     parameters are defaulted as follows.

     MTS.PerMessageSubmissionFields.originator-name
          This is always generated from SMTP, as defined in Chapter 4. |

     MTS.PerMessageSubmissionFields.content-type
          Set to the value implied by the encoding of the IPM (2 or
          22).

     MTS.PerRecipientMessageSubmissionFields.recipient-name
          These will always be supplied from SMTP, as defined in       |
          Chapter 4.

     Optional components are omitted, and default components
     defaulted.  This means that disclosure of recipients is
     prohibited and conversion is allowed.  There are two exceptions
     to the defaulting. For
     MTS.PerMessageSubmissionFields.per-message-indicators, the
     following settings are made:

     -    Alternate recipient is allowed, as it seems desirable to
          maximise the opportunity for (reliable) delivery.            *

     If SMTP is used, Appendix A shall be followed in setting these    |
     parameters.

     MTS.PerMessageSubmissionFields.original-encoded-information-types |
     is derived from the message generated by the gateway, and shall   |
     reflect all body parts.                                           |

     The MTS.PerMessageSubmissionFields.content-correlator is encoded
     as IA5String, and contains the Subject:, Message-ID:, Date:,  and
     To: fields (if present).  This  includes the strings "Subject:",
     "Date:", "To:", "Message-ID:", and appropriate folding to make    |



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     the field appear readable.  This shall be truncated to
     MTS.ub-content-correlator-length (512) characters.  In addition,
     if there is a "Subject:" field, the
     MTS.PerMessageSubmissionFields.content-identifier, is set to a
     printable string representation of the contents of it.   If the
     length of this string is greater than MTS.ub-content-id-length
     (16), it should be truncated to 13 characters and the string
     "..." appended. Both are used, due to the much larger upper bound
     of the content correlator, and that the content id is available
     in X.400(1984).

     5.1.6.  Mappings to the MTA Abstract Service

     There is a need to map directly onto some aspects of the MTA
     Abstract service, for the following reasons:

     -    So the the MTS Message Identifier can be generated from the
          RFC 822 Message-ID:.

     -    So that the submission date can be generated from the
          822.Date.

     -    To prevent loss of trace information

     -    To prevent RFC 822/X.400 looping caused by distribution
          lists or redirects

     The following mappings are defined.

     Message-Id:
          If this is present, the
          MTA.PerMessageTransferFields.message-identifier is generated
          from it, using the mappings described in Chapter 4.

          This mapping arguably generates messages which do not
          conform to US GOSIP (1984 version only), which states:       |











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          6.7.e MPDI Identifier Validation                              |

          (1) Validation of the GlobalDomainIdentifier component of the MPDU|
          Identifier is performed on reception of a message (i.e. the result|
          of a TRANSFER.Indication).                                    |
                                                                        |
          (2) The country name should be known to the validating domain, and|
          depending on the country name, validation of the ADMD name may also|
          be possible.                                                  |

          (3) Additional validation of the GlobalDomainIdentifier is performed|
          against the corresponding first entry in the TraceInformation. If|
          inconsistencies are found during the comparison, a non-delivery|
          notice with the above defined reason and diagnosticcode is    |
          generated.                                                    |

          (4) A request will be generated to the CCITT for a more meaningful|
          diagnostic code (such as "InconsistentMPUTIdentifier").       |


          This applies to ADMDs only, and is specified in the 1984
          version and not the 1988 version. Conformance depends on the
          interpretation of "inconsistency".   The specification makes
          the most sensible choice, and so is not being changed in the
          update from RFC 1327.

     Date:
          This is used to set the first component of
          MTA.PerMessageTransferFields.trace-information
          (MTA.TraceInformationElement).  The SMTP originator is       |
          mapped into an MTS.ORAddress, and used to derive
          MTA.TraceInformationElement.global-domain-identifier.  The
          optional components of
          MTA.TraceInformationElement.domain-supplied-information are
          omitted, and the mandatory components are set as follows:

            MTA.DomainSuppliedInformation.arrival-time
               This is set to the date derived from Date:

            MTA.DomainSuppliedInformation.routing-action
               Set to relayed.

          The first element of



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          MTA.PerMessageTransferFields.internal-trace-information is
          generated in an analogous manner, although this can be
          dropped later in certain circumstances (see the procedures
          for "Received:").  The
          MTA.InternalTraceInformationElement.mta-name is derived from
          the 822.domain in the 822 MTS Originator address.

     Received:
          All RFC 822 trace is used to derive
          MTA.PerMessageTransferFields.trace-information and
          MTA.PerMessageTransferFields.internal-trace-information.
          Processing of Received: lines  follows processing of Date:,
          and is be done from the the bottom to the top of the RFC 822
          header (i.e., in chronological order).  When other trace
          elements (in particular X400-Received:)  are processed the   |
          relative ordering (top to bottom of the header) shall be     |
          retained correctly.  The initial element of
          MTA.PerMessageTransferFields.trace-information will be
          generated already (from Date:), unless the message has
          previously been in X.400, when it will be derived from the
          X.400 trace information.

          Consider the Received: field in question.  If the "by"  part
          of the received is present, use it to derive an
          MTS.GlobalDomainIdentifier.  If this is different from the
          one in the last element of
          MTA.PerMessageTransferFields.trace-information
          (MTA.TraceInformationElement.global-domain-identifier)
          create a new MTA.TraceInformationElement, and optionally
          remove
          MTA.PerMessageTransferFields.internal-trace-information.
          This removal shall be done in cases where the message is
          being transferred to another MD where there is no bilateral
          agreement to preserve internal trace beyond the local MD.
          The trace creation is as for internal trace described below,
          except that no MTA field is needed.                          |

     Editor's Note:                                                    |
          It has been proposed to remove this paragraph, as this       |
          should be done by the MTA beyond the gateway.  Input         |
          solicited.

          Then add a new element (MTA.InternalTraceInformationElement)
          to MTA.PerMessageTransferFields.internal-trace-information,



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          creating this if needed.  This shall be done, even if
          inter-MD trace is created.  The
          MTA.InternalTraceInformationElement.global-domain-identifier
          is set to the value derived.  The
          MTA.InternalTraceInformationElement.mta-supplied-information
          (MTA.MTASuppliedInformation) is set as follows:

            MTA.MTASuppliedInformation.arrival-time
               Derived from the date of the Received: line

            MTA.MTASuppliedInformation.routing-action
               Set to relayed

          The MTA.InternalTraceInformationElement.mta-name is taken
          from the "by" component of the "Received:" field, truncated
          to MTS.ub-mta-name-length (32).  For example:


             Received: from computer-science.nottingham.ac.uk by
                vs6.Cs.Ucl.AC.UK via Janet with NIFTP  id aa03794;
                28 Mar 89 16:38 GMT

     Generates the string

             vs6.Cs.Ucl.AC.UK


     Note that before transferring the message to some ADMDs,
     additional trace stripping may be required, as the implied path
     through multiple MDs would violate ADMD policy.   This will
     depend on bilateral agreement with the ADMD.

          The gateway itself shall not add trace information.
     However, for trace purposes, the gateway shall be considered as
     an X.400 and Internet MTA back to back, and both of these shall
     add trace elements.

     5.1.7.  Mapping New Fields

     This specification defines a number of new fields for Reports,
     Notifications and IP Messages. A gateway conforming to this       |
     specification shall  map all of these fields to X.400, except as  |
     defined below.




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          The mapping of two  extended fields is particularly          |
     important, in order to prevent looping.  "DL-Expansion-History:"
     is mapped to
     MTA.PerMessageTransferFields.extensions.dl-expansion-history
     X400-Received: must be mapped to
     MTA.PerMessageTransferFields.trace-information and
     MTA.PerMessageTransferFields.internal-trace-information.  In
     cases where X400-Received: is present, the usual mapping of Date:
     to generate the first element of trace should not be done.   This
     is because the message has come from X.400, and so the first
     element of trace can be taken from the first X400-Received:.

          The following fields shall not be mapped, and shall be
     discarded:

     -    Discarded-X400-MTS-Extensions:

     -    Message-Type:

     -    Discarded-X400-IPMS-Extensions:

     -    X400-Content-Type:

     -    X400-Originator:

     -    X400-Recipients:

     -    X400-MTS-Identifier:  Mapping this field would be useful in  |
          some circumstances, but very dangerouts in others (e.g.,     |
          following an internet list expansion).  Therefore it is not  |
          mapped.

     5.1.8.  Mapping Delivery Status Notifications to X.400


     5.1.8.1.  Basic Model

     Internet Mail delivery status notifications (DSN) are mapped to
     X.400 delivery reports.   With message mapping, information
     without a mapping is carried by an IPM Extension.   This cannot   |
     be done for delivery reports.   Two mechanisms are used for
     information where there is not a direct mapping.

          The first mechanism is to define extensions, which allow all



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     of the DSN information to be carried in the delivery report.
     This is not completely satisfactory for two reasons:

     1.   User defined extensions are supported by the ISO version of
          the standard, but not the CCITT one.  Therefore,
          implementation support for these extensions will not be
          universal.

     2    X.400 User Agent implementations will not in general
          recognise these extensions.   Therefore, although the
          information will be present, it will often not be available  |
          to the user.    This may be very problematic, as this
          information may be critical to diagnosing the reason for a
          failure.

          Therefore a second mechanism is defined.  This shall always
     be used when the DSN contains non-delivery information, and may
     be used in other cases.  This mechanism is to map the whole DSN   |
     (as if it were an ordinary multipart) into the return of content.
     This will make the DSN information available as a text body part
     in the outer message, with the real returned content as an
     enclosed message.  This mechanism will ensure that information is
     not lost at the gateway.

     5.1.8.2.  DSN Extensions

     Two X.400 MTS extensions are defined as follows:

     dsn-header-list EXTENSION
        RFC822FieldList
        ::= id-dsn-header-list

     dsn-field-list EXTENSION
        RFC822FieldList
        ::= id-dsn-field-list

     The Object Identifiers id-dsn-header-list and id-dsn-field-list   |
     are defined in Appendix D.  These extension is used in the same
     way as the IPM extension rfc-822-field, described in Section      |
     5.1.2.   These extensions may only be used with ISO-10021, and    |
     not X.400 (which does not allow user extensions at the MTS        |
     level).





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     5.1.8.3.  DSN to Delivery Report Mapping

     Reports may not be submitted in the X.400 model, and so the
     report submission is considered in terms of the MTA Abstract
     Service.  An MTA.Report is constructed. The
     MTA.ReportTransferFields.report-identifier is generated from the
     Message-Id of the DSN (if present) and otherwise generated as the
     MTA would generate one for a submitted message.


          The DSN has an RFC 822 header.  Trace is mapped in the same
     manner as for a message to
     MTA.ReportTransferEnvelope.trace-information.  All other headers
     are used to create a dsn-header-list extension, which is added to |
     MTA.ReportTransferFields.extensions.

          The DSN will have a single SMTP recipient.   This is mapped  |
     to the MTA.ReportTransferEnvelope.report-destination-name.

          The DSN is then treated as a normal MIME message, and an
     X.400 IPM is generated.   This IPM is used as
     MTA.PerReportTransferFields.returned-content, and its type is
     used to set MTA.PerReportTransferFields.content-type.  The DSN
     body part is mapped as if it was IA5 text/plain.

          All other mappings are made from the DSN body part. A dsn-
     field-list extension is created and added to
     MTA.ReportTransferFields.extensions.  This is referred to as the
     per report extension list.  The DSN.per-message-fields are mapped
     as follows:

     original-envelope-id-field
          reporting-mta-field                                          |
          dsn-gateway-field                                            |
          received-from-mta-field                                      |
          arrival-date-field                                           |
          extension-field                                              |
          other                                                        |
          All of these fields are added to the per report extension
          list.  Currently there are no other mappings defined.

          Each reported recipient is considered in turn, and a
     MTA.PerRecipientReportTransferFields created for each.  The
     parameters of this are defaulted as follows:



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     originally-specified-recipient-number
          In general, these are not available, and so are assigned
          incrementally.

     last-trace-information
          The arrival-time is generated from DSN.arrival-date if       |
          present, and if not from the Date: of the DSN.

          A dsn-field-list extension is created  and added to
     MTA.PerRecipientTransferFields.extensions.  This is referred to
     as the per recipient extension list.  The
     DSN.per-recipient-fields are mapped as follows

     original-recipient-field
          Mapped to
          MTA.PerRecipientReportTransferFields.originally-intended-recipient-name.

     final-recipient-field
          Mapped to
          MTA.PerRecipientReportTransferFields.actual-recipient-name.

     action-field
          If this is set to "failed", a non-delivery report is
          generated.  Otherwise a delivery report is generated.   Bit
          one or two of
          MTA.PerRecipientTransferFields.per-recipient-indicators is
          set accordingly.  This also controls the encoding of
          MTA.PerRecipientTransferFields.last-trace-information, and
          the selection of the report type.

     status-field
          This is added to the per report extension list.  For non-
          delivery, it is also used to generate the reason and
          diagnostic codes contained within
          MTA.PerRecipientReportTransferFields.last-trace.  The
          mappings are defined below.

     remote-mta-field

     diagnostic-code-field

     last-attempt-date-field

     will-retry-until-field



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     extension-field

     other
          All of these fields are added to the per recipient extension |
          list.

     5.1.8.4.  Status Value Mappings

     Status values are mapped to X.400 reason and diagnostic codes as
     follows.

     DSN code  Meaning                               X400 code Meaning  |

     X.0.0     Other status                          1/None

     X.1.0     Other Address Status                  1/None
     X.1.1     Bad mailbox address                   1/0     Unrecognized
     X.1.2     Bad system address                    1/0     Unrecognized
     X.1.3     Bad mailbox address syntax            1/0     Unrecognized
     X.1.4     Mailbox address ambiguous             1/1

     X.2.0     Other or undefined mailbox status     1/None
     X.2.1     Mailbox disabled, not accepting       1/4     Recipient unavailable
     X.2.2     Mailbox full                          1/4
     X.2.3     Message length exceeds admin limit.   1/7     Content too long
     X.2.4     Mailing list expansion problem        1/30    DL expansion failure

     X.3.0     Other or undefined system status      0/None
     X.3.1     System full                           1/2     MTS congestion
     X.3.2     System not accepting network messages 1/2     MTS congestion
     X.3.3     System not capable of selected feat   1/18    Unsupp. crit. func
     X.3.4     Message too big for system            1/7

     X.4.0     Other or undefined network or routing 0/None
     X.4.1     No answer from host                   0/None
     X.4.2     Bad connection                        0/None
     X.4.3     Routing server failure                6/None  Directory op unsucc.
     X.4.4.    Unable to route                       0/None
     X.4.5     Network congestion                    1/2     MTS congest.
     X.4.6     Routing loop detected                 1/3
     X.4.7     Delivery time expired                 1/5






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     X.5.0     Other or undefined protocol status    1/None

     X.5.1     Invalid command                       1/14    Protocol viol.
     X.5.2     Syntax error                          1/14
     X.5.3     Too many recipients                   1/16
     X.5.4     Invalid command arguments             1/14
     X.5.5     Wrong protocol version                1/18    Unsupp.crit.func

     X.6.0     Other or undefined media error        2/None  Conv. not perf
     X.6.1     Media not supported                   1/6     EIT unsupp.
     X.6.2     Conversion required and prohibited    1/9
     X.6.3     Conversion required but not supported 2/8
     X.6.4     Conversion with loss performed        POSITIVE only

     X.7.0     Other or undefined security status    1/46
     X.7.1     Delivery not authorized, message ref  1/29    No DL submit perm
     X.7.2     Mailing list expansion prohibited     1/28
     X.7.3     Security conversion req but not poss  1/46    Secure mess. error
     X.7.4     Security features not supported       1/46
     X.7.5     Cryptographic failure                 1/46
     X.7.6     Cryptographic algorithm not supported 1/46
     X.7.7     Message integrity failure             1/46



     5.1.8.5.  DSNs that originated in X.400

     The mapping of X.400 delivery reports to DSNs will in general
     provide sufficient information to make a useful reverse mapping.
     Messages will often be mapped multiple times, commonly due to
     forwarding messages and to distribution lists.   Multiple
     mappings for delivery reports will be a good deal less common.
     For this reason, the reverse mapping of the X.400 DSN extensions
     defined in MIXER is optional.

     5.2.  Return of Contents

     It is not clear how widely supported the X.400 return of contents
     service will be.  Experience with X.400(1984) suggests that
     support of this service may not be universal.  As this service is
     expected in the RFC 822 world, two approaches are specified.  The
     choice will depend on the use of X.400 return of contents withing
     the X.400 community being serviced by the gateway.



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          In environments where return of contents is widely
     supported, content return can be requested as a service.  The
     content return service can then be passed back to the end (RFC
     822) user in a straightforward manner.                            *

     5.3.  X.400 -> RFC 822: Detailed Mappings

     5.3.1.  Basic Approach

     A single RFC 822 message is generated from the incoming IP
     Message, Report, or IP Notification.   All IPMS.BodyParts are
     mapped onto a single RFC 822 body.  Other services are mapped
     onto RFC 822 header fields.  Where there is no appropriate
     existing field, new fields are defined for IPMS, MTS and MTA
     services.

          The gateway mechanisms will correspond to MTS Delivery.  As
     with submission, there are aspects where the MTA (transfer)
     services are also used. In particular, there is an optimisation   |
     to allow for multiple SMTP recipients.

     5.3.2.  RFC 822 Settings

     An RFC 822 Message has a number of mandatory fields in the RFC    |
     822 Header.  Some SMTP services mandate specification of an SMTP
     Originator.  Even in cases where this is optional, it is usually
     desirable to specify a value.  The following defaults are
     defined, which shall be used if the mappings specified do not
     derive a value:                                                   |

     SMTP Originator                                                   |
          If this is not generated by the mapping (e.g., for a
          Delivery Report), a value pointing at a gateway
          administrator shall be assigned.

     Date:
          A value will always be generated

     From:
          If this is not generated by the mapping, it is assigned
          equal to the SMTP Originator.  If this is gateway generated, |
          an appropriate 822.phrase shall be added.

     At least one recipient field



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          If no recipient fields are generated, a field "To: list:;",
          shall be added.

     This will ensure minimal RFC 822 compliance.  When generating RFC
     822 headers, folding may be used.  It is recommended to do this,
     following the guidelines of RFC 822.

     5.3.3.  Basic Mappings

     5.3.3.1.  Encoded Information Types

     This mapping from MTS.EncodedInformationTypes is needed in
     several disconnected places.  EBNF is defined as follows:

             encoded-info    = 1#encoded-type

             encoded-type    = built-in-eit / object-identifier

             built-in-eit    = "Undefined"         ; undefined (0)
                             / "Telex"             ; tLX (1)
                             / "IA5-Text"          ; iA5Text (2)
                             / "G3-Fax"            ; g3Fax (3)
                             / "TIF0"              ; tIF0 (4)
                             / "Teletex"           ; tTX (5)
                             / "Videotex"          ; videotex (6)
                             / "Voice"             ; voice (7)
                             / "SFD"               ; sFD (8)
                             / "TIF1"              ; tIF1 (9)


     MTS.EncodedInformationTypes is mapped onto EBNF.encoded-info.
     MTS.EncodedInformationTypes.non-basic-parameters is ignored.
     Built in types are mapped onto fixed strings (compatible with
     X.400(1984) and RFC 987), and other types are mapped onto
     EBNF.object-identifier.

     5.3.3.2.  Global Domain Identifier

     The following simple EBNF is used to represent
     MTS.GlobalDomainIdentifier:

             global-id = std-or-address

     This is encoded using the std-or-address syntax, for the



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     attributes within the Global Domain Identifier.

     5.3.4.  Mappings from the IP Message

     Consider that an IPM has to be mapped to RFC 822.  The IPMS.IPM
     comprises an IPMS.IPM.heading and IPMS.IPM.body.   The heading is
     considered first.  Some EBNF for new fields is defined:

             ipms-field = "Obsoletes" ":" 1#msg-id
                        / "Expiry-Date" ":" date-time
                        / "Reply-By" ":" date-time
                        / "Importance" ":" importance
                        / "Sensitivity" ":" sensitivity
                        / "Autoforwarded" ":" boolean
                        / "Incomplete-Copy" ":"
                        / "Content-Language" ":" 1#language             |
                        / "Message-Type" ":" message-type
                        / "Discarded-X400-IPMS-Extensions" ":" 1#object-identifier
                        / "Autosubmitted" ":" autosubmitted



             importance      = "low" / "normal" / "high"


             sensitivity     = "Personal" / "Private" /
                                    "Company-Confidential"

             language        = 2*ALPHA [ language-description ]
             language-description = printable-string



             message-type    = "Delivery Report"
                             / "InterPersonal Notification"
                             / "Multiple Part"



             autosubmitted   = "not-auto-submitted"
                             / "auto-generated"
                             / "auto-replied"
                             / "auto-forwarded"




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     The mappings and actions for the IPMS.Heading are now specified   |
     for each element.  Addresses and Message Identifiers are mapped
     according to Chapter 4.  Other mappings are explained, or are
     straightforward (algorithmic).  If a field with addresses
     contains zero elements, it should be discarded, except for
     IPMS.Heading.blind-copy-recipients, which can be mapped onto BCC:
     (the only RFC 822 field which allows zero recipients).

     IPMS.Heading.this-IPM
          Mapped to "Message-ID:".

     IPMS.Heading.originator
          If IPMS.Heading.authorizing-users is present this is mapped
          to Sender:, if not to "From:".

     IPMS.Heading.authorizing-users
          Mapped to "From:".

     IPMS.Heading.primary-recipients
          Mapped to "To:".

     IPMS.Heading.copy-recipients
          Mapped to "Cc:".

     IPMS.Heading.blind-copy-recipients
          Mapped to "Bcc:".

     IPMS.Heading.replied-to-ipm
          Mapped to "In-Reply-To:".

     IPMS.Heading.obsoleted-IPMs
          Mapped to the extended RFC 822 field "Obsoletes:"

     IPMS.Heading.related-IPMs
          Mapped to "References:".

     IPMS.Heading.subject
          Mapped to "Subject:".  The contents are converted to ASCII
          or T.61 (as defined in Section 3.5).  Any CRLF are not
          mapped, but are used as points at which the subject field
          must be folded.

     IPMS.Heading.expiry-time
          Mapped to the extended RFC 822 field "Expiry-Date:".



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     IPMS.Heading.reply-time
          Mapped to the extended RFC 822 field "Reply-By:".

     IPMS.Heading.reply-recipients
          Mapped to "Reply-To:".

     IPMS.Heading.importance
          Mapped to the extended RFC 822 field "Importance:".

     IPMS.Heading.sensitivity
          Mapped to the extended RFC 822 field "Sensitivity:".

     IPMS.Heading.autoforwarded
          Mapped to the extended RFC 822 field "Autoforwarded:".

     The standard extensions (Annex H of X.420 / ISO 10021-7) are
     mapped as follows:

     incomplete-copy
          Mapped to the extended RFC 822 field "Incomplete-Copy:".

     language
          Mapped to the  RFC 822 field "Content-Language:", defined in
          RFC 1766 [8].  This mapping may be made without loss of
          information.

     auto-submitted
          Map to the extended RFC 822 field "Autosubmitted:".

          If the RFC 822 extended header is found, this shall be
     mapped onto an RFC 822 header, as described in Section 5.1.2.

          If a non-standard extension is found, it shall be discarded,
     unless the gateway understands the extension and can perform an
     appropriate mapping onto an RFC 822 header field.  If extensions
     are discarded, the list is indicated in the extended RFC 822
     field "Discarded-X400-IPMS-Extensions:".

     5.3.4.1.  Mapping the IPMS Body

     The IPMS.Body is mapped into the RFC 822 message body.  If the
     IPMS.Body consists of a single IPMS.Bodypart, there are three
     possibilities.




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     1.   If it is of type IPMS.IA5Text, then this is mapped directly
          and no MIME encoding is used.

     2.   If it is of type IPMS.MessageBodyPart, then a MIME message
          with content type message/rfc822 is generated, following the
          mappings described for IPMS.BodyPart given below, except in  |
          the case where a multipart-message heading extension is      |
          present.   In the latter case the mapping of 5.1 shall be    |
          reversed.

     3.   The mapping of other body parts is specified below.

     If the IPMS.Body contains multiple IPMS.BodyPart fields, then a
     MIME message of content type multipart is generated.  If all of
     the body parts are messages, then this is multipart/digest.
     Otherwise it is multipart/mixed.  The components of the multipart
     are generated in the same order as in the IPMS.Body.   Body parts
     which are not messages are mapped according to RFC 1494bis.       |

          To map an IPMS.MessageBodyPart, the full X.400 -> RFC 822
     mapping  is recursively applied, to generate an RFC 822 Message.
     If present, the IPMS.MessageBodyPart.parameters.delivery-envelope
     is used for the MTS Abstract Service Mappings.  If present, the
     IPMS.MessageBodyPart.parameters.delivery-time is mapped to the
     extended RFC 822 field "Delivery-Date:".

          To support X.400(1984) mappings of Internet Messages, the
     following procedure shall also be followed.  If there is more
     than one body part, and the first body part is IA5 starts with
     the string "RFC-822-Headers:" as the first line, then the
     remainder of this body part shall be appended to the RFC 822      |
     header.  This relies that this body part has been generated       |
     according to Appedix B of MIXER.  A gateway shall check the       |
     consistency and syntax of this body part, to ensure that the      |
     resulting message is conformant.

     5.3.4.2.  Mapping Body Parts

     X.400 and MIME  define  extensible approaches for body parts, and
     the ability to map a specific body part depends on the gateway's
     knowledge.  Mapping of all standard X.400 body parts, and some
     extended body parts is defined in RFC 1494bis.

          The case of File Transfer Body Part (FTBP) is described



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     below.

          Where no mapping is known by the gateway, it may choose to
     drop the body part, or reject the message.   It may also
     encapsulate the body part in a mechanism which can be used for
     any extended X.400 body part.  This is specified below.  The
     option will depend on the gateway configuration and its knowledge
     of the recipient capabilities.

     5.3.4.3.  File Transfer Body Part

     X.400 specifies a file transfer body part (FTBP).  Generic
     mapping of FTBP is beyond the scope of MIXER.   EMA have defined
     a profile of FTBP to carry attachments [28].  MIXER defines a
     mapping of FTBP to MIME, which is intended for use in conjunction
     with this profile.   FTBP is used to carry various pieces of
     information associated with an attachment.  The key mapping will
     be to correctly convert the contents of the attachment.  This
     specification also provides a mechanism for mapping the
     parameters which EMA have recommended to be used in version 1.4
     of the specification.  A BNF is defined below:

     ftbp-field = "FTBP-Object-Size" ":" integer                        |
                / "FTBP-Creation-Date" ":" date-time
                / "FTBP-Modification-Date" ":" date-time
                  "FTBP-Read-Date" ":" date-time


          Some parameters are encoded as graphical strings.  To map    |
     these to ASCII, those characters that map directly are mapped,
     and others are translated to "?".   This simple non-reversible
     mapping is seen as appropriate for the application, and in line
     with the spirit of the EMA profile.

          Mapping of the data will be dependent on the attachment, its
     encoding, and the MIME representation.   These cannot be
     specified here.

          Other FTBP Parameters are mapped as follows:

     FileTransferParameters.environment.user-visible-string
          This is mapped to the "Content-Descriptor:" header.

     The following elements of FileTransferParameters.file-attributes



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     are mapped as follows:

     pathname
          Mapped to "Content-Dispostion:", as defined in RFC 1806      |
          [33].  The EBNF.disposition-type is set to "attachment", and |
          the filename is included as a parameter.  For example:       |

                  Content-Disposition: attachment; filename=/var/joe/dodo.doc

          It is expected that only the incomplete option will be
          found, but the mapping is used for either variant.  The
          separator between multiple components is "/".

     date-and-time-of-creation
          Mapped to "FTBP-Creation-Date:".

     date-and-time-of-last-modification
          Mapped to "FTBP-Modification-Date:".

     date-and-time-of-last-read-access
          Mapped to "FTBP-Read-Date:".

     object-size
          Mapped to "FTBP-Object-Size:".

     5.3.4.4.  Tunnelling X.400 Body Parts

     This section specifies a generic mechanism to map X.400 body
     parts to a MIME content.  This allows for the body part to be
     tunnelled through MIME.   It may also be used directly by an
     appropriately configured MIME UA.

          This content-type is defined to carry any X.400 extended
     body part.  The mapping of all standard X.400 body parts is
     defined in RFC1494bis.  The content-type field is
     "application/x400-bp".  The parameter is defined by the EBNF:

             mime-parameter =  "bp-type=" object-identifier


          The EBNF.object-identifier is set to the OBJECT IDENTIFIER
     from IPMS.body.externally-defined.data.direct-reference .

     For example, a Videotex body part will have



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             Content-type=application/x400-bp; bp-type=2.6.1.4.5


          The body contains the raw ASN.1 IPM.body octet stream,
     including the initial tag octet.  The content may use a content-
     transfer-encoding of either base64 or quoted-printable when
     carried in 7-bit MIME.  It is recommended to use the one which
     gives the more compact encoding of the data.  If this cannot be
     determined, Base64 is recommended.  No attempt is made to turn
     the parameters of Extended Body Parts into MIME parameters, as
     this cannot be done in a general manner.

          Standard X.400 body parts may not be encoded directly by
     this mechanism, but may be encoded indirectly by first
     translating to the extended representation.                       *

     5.3.4.5.  Example Message

     An example message, illustrating a number of aspects is given
     below.


























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MIXER                                                DRAFT Version 2.2



     Received: from mhs-relay.ac.uk by bells.cs.ucl.ac.uk via JANET with NIFTP
               id <7906-0@bells.cs.ucl.ac.uk>; Thu, 30 May 1991 18:24:55 +0100
     X400-Received: by mta "mhs-relay.ac.uk" in /PRMD=uk.ac/ADMD= /C=gb/; Relayed;
                    Thu, 30 May 1991 18:23:26 +0100
     X400-Received: by /PRMD=HMG/ADMD=GOLD 400/C=GB/; Relayed;
                    Thu, 30 May 1991 18:20:27 +0100
     Message-Type: Multiple Part
     Date: Thu, 30 May 1991 18:20:27 +0100
     X400-Originator: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
     X400-MTS-Identifier:
          [/PRMD=HMG/ADMD=GOLD 400/C=GB/;PC1000-910530172027-57D8]
     Original-Encoded-Information-Types: ia5                            |
     X400-Content-Type: P2-1984 (2)
     X400-Content-Identifier: Email Problems
     From: Stephen.Harrison@gosip-uk.hmg.gold-400.gb (Tel +44 71 217 3487)
     Message-ID: <PC1000-910530172027-57D8*@MHS>
     To: Jim Craigie <NTIN36@gec-b.rutherford.ac.uk>,
         Tony Bates <tony@ean-relay.ac.uk>,
         Steve Kille <S.Kille@cs.ucl.ac.uk>
     Subject: Email Problems
     Sender: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
     MIME-Version: 1.0
     Content-Type: multipart/mixed; boundary=boundary-1

     --boundary-1
     Content-Type: text/plain; charset=US-ASCII

     Hope you gentlemen.......

     Regards,

     Stephen Harrison
     UK GOSIP Project

      ..... continued on next page











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     --boundary-1
     Content-Type: message/rfc822

     From: Urs Eppenberger <Eppenberger@verw.switch.ch>
     Message-ID:
       <562*/S=Eppenberger/OU=verw/O=switch/PRMD=SWITCH/ADMD=ARCOM/C=CH/@MHS>
     To: "Stephen.Harrison" <Stephen.Harrison@gosip-uk.hmg.gold-400.gb>
     Cc: kimura@bsdarc.bsd.fc.nec.co.jp
     Subject: Response to Email link
     Content-Type: multipart/mixed; boundary=boundary-2


     --boundary-2

     Dear Mr Harrison......


     --boundary-2--                                                     |

     --boundary-1--                                                     |



     5.3.5.  Mappings from an IP Notification

     Because of the service setting, IP Notifications will not usually |
     need to be mapped by a MIXER gateway.  A message is generated,
     with the following fields:

     From:
          Set to the IPMS.IPN.ipn-originator.

     To:  Set to the recipient from MTS.MessageSubmissionEnvelope.
          If there have been redirects, the original address should be
          used.

     Subject:
          Set to the string  "X.400 Inter-Personal Notification" for a
          receipt notification and to "X.400 Inter-Personal
          Notification (failure)" for a non-receipt notification.

     Message-Type:



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MIXER                                                DRAFT Version 2.2


          Set to "InterPersonal Notification"

     References:
          Set to IPMS.IPN.subject-ipm

     Discarded-X400-IPMS-Extensions:
          Used for any discarded IPN extensions.

     The following EBNF is defined for the body of the Message.  This
     format is defined to ensure that all information from an
     interpersonal notification is available to the end user in a
     uniform manner.



































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MIXER                                                DRAFT Version 2.2



             ipn-body-format = ipn-description <CRLF>
                             [ ipn-extra-information <CRLF> ]
                             [ ipn-content-return ]

             ipn-description = ipn-receipt / ipn-non-receipt

             ipn-receipt = "Your message to:" preferred-recipient <CRLF>
                      "was received at" receipt-time <CRLF> <CRLF>
                      "This notification was generated"
                      acknowledgement-mode <CRLF>
                      "The following extra information was given:" <CRLF>
                      ipn-suppl <CRLF>

             ipn-non-receipt "Your message to:"
                     preferred-recipient <CRLF>
                     ipn-reason


             ipn-reason = ipn-discarded / ipn-auto-forwarded

             ipn-discarded = "was discarded for the following reason:"
                             discard-reason <CRLF>

             ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                             [ "The following comment was made:"
                                     auto-comment ]


             ipn-extra-information =
                      "The following information types were converted:"
                      encoded-info

             ipn-content-return = "The Original Message is not available"
                             / "The Original Message follows:"


             preferred-recipient = mailbox
             receipt-time        = date-time
             auto-comment        = printablestring
             ipn-suppl           = printablestring






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             discard-reason     = "Expired" / "Obsoleted" /
                                     "User Subscription Terminated"

             acknowledgement-mode = "Manually" / "Automatically"

     The mappings for elements of the common fields of IPMS.IPN
     (IPMS.CommonFields) onto this structure and the message header
     are:

     subject-ipm
          Mapped to "References:"

     ipn-originator
          Mapped  to "From:".

     ipn-preferred-recipient
          Mapped to EBNF.preferred-recipient

     conversion-eits
          Mapped to EBNF.encoded-info in EBNF.ipn-extra-information

     The mappings for elements of IPMS.IPN.non-receipt-fields
     (IPMS.NonReceiptFields) are:

     non-receipt-reason
          Used to select between EBNF.ipn-discarded and
          EBNF.ipn-auto-forwarded

     discard-reason
          Mapped to EBNF.discard-reason

     auto-forward-comment
          Mapped to EBNF.auto-comment

     returned-ipm
          This applies only to non-receipt notifications.
          EBNF.ipn-content-return should always be omitted for receipt
          notifications, and always be present in non-receipt
          notifications.  If present, the second option of
          EBNF.ipn-content-return is chosen, and the message is
          included.  In this case, the message is formatted as
          multipart/mixed, and the returned message included as
          message/rfc822 after the text body part. Otherwise the first



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          option is chosen.

     The mappings for elements of IPMS.IPN.receipt-fields
     (IPMS.ReceiptFields) are:

     receipt-time
          Mapped to EBNF.receipt-time

     acknowledgement-mode
          Mapped to EBNF.acknowledgement-mode

     suppl-receipt-info
          Mapped to EBNF.ipn-suppl

     An example notification is:

             From: Steve Kille <steve@cs.ucl.ac.uk>
             To: Julian Onions <jpo@computer-science.nottingham.ac.uk>
             Subject: X.400 Inter-personal Notification
             Message-Type: InterPersonal Notification
             References: <1229.614418325@UK.AC.NOTT.CS>
             Date: Wed, 21 Jun 89 08:45:25 +0100

             Your message to: Steve Kille <steve@cs.ucl.ac.uk>
             was automatically forwarded.
             The following comment was made:
                     Sent on to a random destination

             The following information types were converted: g3fax



     5.3.6.  Mappings from the MTS Abstract Service

     This section describes the MTS mappings for User Messages (IPM
     and IPN).  This mapping is defined by specifying the mapping of
     MTS.MessageDeliveryEnvelope.  The following extensions to RFC 822
     are defined to support this mapping:









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MIXER                                                DRAFT Version 2.2



             mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                       / "X400-Originator" ":" mailbox
                       / "X400-Recipients" ":" 1#mailbox
                       / "Original-Encoded-Information-Types" ":"
                                       encoded-info
                       / "X400-Content-Type" ":" mts-content-type
                       / "Content-Identifier" ":" printablestring
                       / "Priority" ":" priority
                       / "Originator-Return-Address" ":" 1#mailbox
                       / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                       / "Conversion" ":" prohibition
                       / "Conversion-With-Loss" ":" prohibition
                       / "Requested-Delivery-Method" ":"
                                       1*( labelled-integer )
                       / "Delivery-Date" ":" date-time
                       / "Discarded-X400-MTS-Extensions" ":"
                                    1#( object-identifier / labelled-integer )


             prohibition     = "Prohibited" / "Allowed"

             mts-msg-id       = "[" global-id ";" *text "]"

             mts-content-type = "P2" /  labelled-integer
                             / object-identifier

             priority        = "normal" / "non-urgent" / "urgent"


     The mappings for each element of MTS.MessageDeliveryEnvelope can
     now be considered.

     MTS.MessageDeliveryEnvelope.message-delivery-identifier
          Mapped to the extended RFC 822 field "X400-MTS-Identifier:".

     MTS.MessageDeliveryEnvelope.message-delivery-time
          Discarded, as this time will be represented in an
          appropriate trace element.

     The mappings for elements of
     MTS.MessageDeliveryEnvelope.other-fields
     (MTS.OtherMessageDeliveryFields) are:




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MIXER                                                DRAFT Version 2.2


     content-type
          Mapped to the extended RFC 822 field "X400-Content-Type:".
          The string "P2" is retained for backwards compatibility with
          RFC 987. This shall not be generated, and either the
          EBNF.labelled-integer  or EBNF.object-identifier encoding
          used.

     originator-name
          Mapped to the SMTP originator, and to the extended RFC 822   |
          field "X400-Originator:".  This is described in
          Section 4.6.2.

     original-encoded-information-types
          Mapped to the extended RFC 822 field
          "Original-Encoded-Information-Types:".

     priority
          Mapped to the extended RFC 822 field "Priority:".

     delivery-flags
          If the conversion-prohibited bit is set, add an extended RFC
          822 field "Conversion:".

     this-recipient-name and other-recipient-names

     originally-intended-recipient-name
          The handling of these elements is described in
          Section 4.6.2.

     converted-encoded-information-types
          Discarded.  This information will be mapped in the trace.    |

     message-submission-time
          Mapped to Date:.

     content-identifier
          Mapped to the extended RFC 822 field
          "X400-Content-Identifier:".  In RFC 1327, this was
          "Content-Identifier:".  This has been changed to avoid
          confusion with MIME defined fields.   Gateways which reverse
          map, may support the old field.

     If any extensions
     (MTS.MessageDeliveryEnvelope.other-fields.extensions) are



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     present, and they are marked as critical for transfer or
     delivery, then the message shall be rejected.  The extensions
     (MTS.MessageDeliveryEnvelope.other-fields.extensions) are mapped
     as follows.

     conversion-with-loss-prohibited
          If set to
          MTS.ConversionWithLossProhibited.conversion-with-loss-prohibited,
          then add the extended RFC 822 field "Conversion-With-Loss:".

     requested-delivery-method
          Mapped to the extended RFC 822 field
          "Requested-Delivery-Method:".

     originator-return-address
          Mapped to the extended RFC 822 field
          "Originator-Return-Address:".

     physical-forwarding-address-request
     physical-delivery-modes
     registered-mail-type
     recipient-number-for-advice
     physical-rendition-attributes
     physical-delivery-report-request
     physical-forwarding-prohibited


          These elements are only appropriate for physical delivery.
          They are represented as comments in the "X400-Recipients:"
          field, as described in Section 4.6.2.2.

     originator-certificate
     message-token
     content-confidentiality-algorithm-identifier
     content-integrity-check
     message-origin-authentication-check
     message-security-label
     proof-of-delivery-request

          These elements imply use of security services not available
          in the RFC 822 environment.  If they are marked as critical
          for transfer or delivery, then the message shall be
          rejected.  Otherwise they are discarded.




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     redirection-history
          This is described in Section 4.6.2.

     dl-expansion-history
          Each element is mapped to the extended RFC 822 field
          "DL-Expansion-History:".  They shall be ordered in the
          message header, so that the most recent expansion comes
          first (same order as trace).

          If any MTS (or MTA) Extensions not specified in X.400 are
     present, and they are marked as critical for transfer or
     delivery, then the message shall be rejected.  If they are not so
     marked, they can safely be discarded.  The list of discarded
     fields shall be indicated in the extended header
     "Discarded-X400-MTS-Extensions:".

     5.3.7.  Mappings from the MTA Abstract Service

     There are some mappings at the MTA Abstract Service level which
     are done for IPM and IPN.  These can be derived from
     MTA.MessageTransferEnvelope.  The reasons for the mappings at
     this level, and the violation of layering are:

     -    Allowing for multiple recipients to share a single RFC 822
          message

     -    Making the X.400 trace information available on the RFC 822
          side

     -    Making any information on deferred delivery available

     The SMTP recipients are calculated from the full list of X.400    |
     recipients.  This is all of the members of
     MTA.MessageTransferEnvelope.per-recipient-fields being passed
     through the gateway, where the responsibility bit is set.  In
     some cases, a different RFC 822 message would be calculated for
     each recipient, due to differing service requests for each
     recipient.  As discussed in 4.6.2.2, this specification allows
     either for multiple messages to be generated, or for the per-
     recipient information to be discarded.

     The following EBNF is defined for extended RFC 822 headers:





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RFC 1327bis
MIXER                                                DRAFT Version 2.2




             mta-field       = "X400-Received" ":" x400-trace
                             / "Deferred-Delivery" ":" date-time
                             / "Latest-Delivery-Time" ":" date-time



             x400-trace       = "by" md-and-mta ";"
                              [ "deferred until" date-time ";" ]
                              [ "converted" "(" encoded-info ")" ";" ]
                              [ "attempted" md-or-mta ";"  ]
                                 action-list
                                 ";" arrival-time


             md-and-mta       = [ "mta" mta "in" ]  global-id
             mta              = word
             arrival-time     = date-time

             md-or-mta        = "MD" global-id
                              / "MTA" mta

             Action-list      = 1#action
             action           = "Redirected"
                              / "Expanded"
                              / "Relayed"
                              / "Rerouted"




          Note the EBNF.mta is encoded as 822.word.  If the character  |
     set does not allow encoding as 822.atom, the 822.quoted-string
     encoding is used.

          If MTA.PerMessageTransferFields.deferred-delivery-time is
     present, it is used to generate a Deferred-Delivery: field.  For
     some reason, X.400 does not make this information available at
     the MTS level on delivery.  X.400 profiles, and in particular the
     CEN/CENELEC profile for X.400(1984) [32], specify that this
     element must be supported at the first MTA.  If it is not, the
     function may optionally be implemented by the gateway: that is,
     the gateway may hold the message until the time specified in the



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     protocol element.  Thus, the value of this element will usually
     be in the past.  For this reason, the extended RFC 822 field is
     primarily for information.

          Merge MTA.PerMessageTransferFields.trace-information, and
     MTA.PerMessageTransferFields.internal-trace-information to
     produce a single ordered trace list.  If Internal trace from
     other management domains has not been stripped, this may require
     complex interleaving. Where an element of internal trace and
     external trace are identical, except for the MTA in the internal
     trace, only the internal trace element shall be presented. Use
     this to generate a sequence of "X400-Received:" fields. The only
     difference between external trace and internal trace will be the
     extra MTA information in internal trace elements.

          When generating an RFC 822 message all trace fields (X400-
     Received and Received) shall be at the beginning of the header,
     before any other fields.  Trace shall be in chronological order,
     with the most recent element at the front of the message.  This
     ordering is determined from the order of the fields, not from
     timestamps in the trace, as there is no guarantee of clock
     synchronisation.  A simple example trace (external) is:

     X400-Received: by /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; Relayed ;
             Tue, 20 Jun 89 19:25:11 +0100

     A more complex example (internal):

     X400-Received: by mta "UK.AC.UCL.CS" in  /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ;
             deferred until  Tue, 20 Jun 89 14:24:22 +0100 ;
             converted (undefined, g3fax) ; attempted /ADMD=Foo/C=GB/ ;
             Relayed, Expanded, Redirected ; Tue, 20 Jun 89 19:25:11 +0100


          The gateway itself shall not add trace information.
     However, for trace purposes, the gateway shall be considered as
     an X.400 and Internet MTA back to back, and both of these shall
     add trace elements.

     5.3.8.  Mappings from Report Delivery

     Delivery reports are mapped at the MTS service level.  This means
     that only reports destined for the MTS user will be mapped.  Some
     additional services are also taken from the MTA service.  X.400



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RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Delivery Reports are Mapped onto Delivery Status Notifications,
     as defined by NOTARY [29].

     5.3.8.1.  MTS Mappings

     A Delivery Report service will be represented as
     MTS.ReportDeliveryEnvelope, which comprises of per-report-fields
     (MTS.PerReportDeliveryFields) and per-recipient-fields.

     A message of type delivery-status is generated with the following
     fields:

     From:
          An administrator at the gateway system.  This is also the    |
          SMTP originator.

     To:  A mapping of the
          MTA.ReportTransferEnvelope.report-destination-name.  This is |
          also the SMTP recipient.

     Message-Type:
          Set to "Delivery Report".  This is strictly redundant, but
          retained for backwards compatibility with RFC 1327.

     Subject:
          The EBNF for the subject line is:


             subject-line  = "Delivery-Report" "(" status ")"
                             [ "for" destination ]

             status        = "success" / "failure" / "success and failures"

             destination   = mailbox / "MTA" word


          The subject is intended to give a clear indication as to the
     nature of the message, and summarise its contents. EBNF.status is
     set according to whether the reports are all successes, all
     failures, or a mixture.  The EBNF.destination is used to indicate
     the addresses in the reports.  If the report is for a single
     address, EBNF.mailbox is used to give the RFC 822 representation
     of the address.  If all of the reports share a common MTA this is
     included in EBNF.word.   A common MTA is determined from the



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RFC 1327bis
MIXER                                                DRAFT Version 2.2


     delivery report's trace.

          The format of the body of the message follows the NOTARY
     delivery status notification format, and is defined to ensure
     that all information is conveyed to the RFC 822 user in a
     consistent manner.  The format is structured as if it was a
     message coming from the gateway, with three body parts. The first
     body part is ASCII text structured as follows:

     1.   A few lines giving keywords to indicate the original
          message.

     2.   A human summary of the status of each recipient being
          reported on.

          The second  body part is the NOTARY delivery status
     notification, which contains detailed information extracted from
     the report.  This information may be critical to diagnosing an
     obscure problem.

          This body part may be omitted in positive DRs.  For RFC
     1327, this was recommended as appropriate for most gateways.  As
     NOTARY becomes more widely adopted, this will make less sense.
     It is likely that this body part will be mandatory in future
     versions of this specification.

          The third (optional) body part contains the returned message
     (return of content).  This structure is useful to the RFC 822
     recipient, as it enables the original message to be extracted.
     It shall be included if the original message is available.

          The enclosing message is a MIME message of content type
     multipart/report, with report-type=delivery-status.  The first
     body part containing the user oriented description is of type
     text/plain.  The format of this body part is defined below as
     EBNF.dr-user-info.











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             dr-user-info = dr-summary <CRLF>
                             dr-recipients <CRLF>
                             dr-content-return


             dr-content-return = "The Original Message is not available"
                  / "The Original Message follows:"

             dr-summary = "This report relates to your message:" <CRLF>
                             content-correlator <CRLF> <CRLF>
                          "of" date-time <CRLF> <CRLF>


             dr-recipients = *(dr-recipient <CRLF> <CRLF>)

             dr-recipient = dr-recip-success / dr-recip-failure

             dr-recip-success =
                             "Your message was successfully delivered to:"
                              mailbox "at" date-time


             dr-recip-failure = "Your message was not delivered to:"
                                     mailbox <CRLF>
                             "for the following reason:" *word

             report-point = [ "mta" word "in" ] global-id
             content-correlator = *word


     EBNF.dr-summary
          The EBNF.content-correlator is taken from the content
          correlator (or content identifier if there is no content
          correlator) and the EBNF.date-time from the trace, as
          described below.  LWSP may be added to improve the layout of
          the body part.

     EBNF.dr-recipients
          There is an element for each recipient in the delivery
          report.  In each case, EBNF.mailbox is taken from the RFC
          822 form of the originally specified recipient, which is
          taken from the originally specified recipient element if
          present or from the actual recipient.  When reporting



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          success, the message delivery time is used to derive
          EBNF.date-time.  When reporting failure, the information
          includes a human readable interpretation of the X.400
          diagnostic and reason codes, and the supplementary
          information.

     EBNF.dr-content-return
          This is set according to whether or not the content is being
          returned.

     The EBNF of this body part is designed for english-speaking
     users.  The language of the strings in the EBNF may be altered.

     The EBNF used in the delivery status notification is:


             dr-per-message-fields =
                       / "X400-Conversion-Date" ":" date-time
                       / "X400-Subject-Submision-Identifier" ":"
                                             mts-msg-id
                       / "X400-Content-Identifier" ":" printablestring
                       / "X400-Content-Type" ":" mts-content-type
                       / "X400-Original-Encoded-Information-Types" ":"
                                     encoded-info
                       / "X400-Originator-and-DL-Expansion-History" ":"
                                     dl-history
                       / "X400-Reporting-DL-Name" ":" mailbox
                       / "X400-Content-Correlator" ":" content-correlator
                       / "X400-Recipient-Info" ":" recipient-info
                       / "X400-Subject-Intermediate-Trace-Information" ":"
                                               x400-trace
                       / dr-extensions















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RFC 1327bis
MIXER                                                DRAFT Version 2.2



             dr-per-recipient-fields =
                       / "X400-Redirect-Recipient" ":" "x400" ";" std-or
                       / "X400-Mapped-Redirect-Recipient" ":" "rfc822" ";" mailbox
                       / "X400-Converted-EITs" ":" encoded-info ";"
                       / "X400-Delivery-Time" ":" date-time
                       / "X400-Type-of-MTS-User" ":" labelled-integer
                       / "X400-Last-Trace" ":" [ encoded-info ] date-time
                       / "X400-Supplementary-Info" ":"
                             <"> printablestring <"> ";"
                       / "X400-Redirection-History" ":" redirection-comment
                       / "X400-Physical-Forwarding-Address" ":" printablestring
                       / "X400-Originally-Specified-Recipient-Number" ":"
                             integer
                       / dr-extensions

             dr-extensions = "X400-Discarded-DR-Extensions" ":"
                               1# (object-identifier / labelled-integer)


             dl-history = 1#( mailbox "(" date-time ")")

                       / "X400-Diagnostic" ":" labelled-integer
                       / "X400-Reason" ":" labelled-integer

             dr-diagnostic = "Reason" labelled-integer
                             [ ";" "Diagnostic" labelled-integer ]


     A body part of type delivery status, as defined by NOTARY, is
     generated.  MIXER extends this delivery status notification (DSN)
     specification, by defining additional per message fields in
     EBNF.dr-per-message-fields and additional per recipient fields in
     EBNF.dr-per-recipient-fields.   These are used as extensions to
     DSN.per-message-fields and DSN.per-recipient-fields.

     The following DSN.per-message-fields are always generated:

     DSN.reporting-mta-field
          The DSN.mta-name-type is set to "x400", and this string is
          reserved by MIXER.  The DSN.mta-name has its syntax
          specified by EBNF.report-point, with the information derived
          from the first element of the DR's trace.




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     DSN.arrival-date-field
          This is derived from the date of the first element of trace
          in the DR.

          The following two EBNF.per-message-fields are generated by
     the MIXER gateway:

     DSN.dsn-gateway-field
          The type is set to "dns" and the  domain  set to the local
          domain of the gateway.

     X400-Conversion-Date:
          The EBNF.date-time is set to the time of the MIXER
          conversion.

          The elements of MTS.ReportDeliveryEnvelope.per-report-fields
     are mapped as follows onto the DSN per message fields as follows:

     subject-submission-identifier
          Mapped to DSN.original-envelope-id-field.  The encoding of
          this MTS Identifier follows the format EBNF.mts-msg-id.

     content-identifier
          Mapped to X400-Content-Identifier:

     content-type
          Mapped to X400-Content-Type:

     original-encoded-information-types
          Mapped to X400-Encoded-Info:

     The extensions from
     MTS.ReportDeliveryEnvelope.per-report-fields.extensions are
     mapped as follows:

     originator-and-DL-expansion-history
          Mapped to X400-Originator-and-DL-Expansion-History:

     reporting-DL-name
          Mapped to X400-Reporting-DL-Name:

     content-correlator
          Mapped to X400-Content-Correlator:, provided that the
          encoding is IA5String (this will always be the case).



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     message-security-label
     reporting-MTA-certificate
     report-origin-authentication-check

          These security parameters will not be present unless there
          is an error in a remote MTA.  If they are present, they
          shall be discarded in preference to discarding the whole
          report.  They shall be listed in the X400-Discarded-DR-
          Extensions: field.

     If there are any other DR extensions, they shall also be
     discarded and listed in the X400-Discarded-DR-Extensions: field.

     For each element of
     MTS.ReportDeliveryEnvelope.per-recipient-fields, a set of
     DSN.per-recipient-fields is generated.  The fields are filled in
     as follows:

     actual-recipient-name
          If originally-intended-recipient-name is not present,        |
          generate a DSN.final-recipient-field fields, with            |
          DSN.address-type of "rfc822", and with an RFC 822 mailbox
          generated from the address encoded as specified by NOTARY.
          Also generate a DSN.original-recipient-field field, which
          holds the X.400 representation of the same address.  If the
          directory name is present, it should be added as a trailing
          comment in the X.400 form.

          If originally-intended-recipient-name is present, generate   |
          an "X400-Mapped-Redirect-Recipient:" field, with             |
          DSN.address-type of "rfc822", and with an RFC 822 mailbox
          generated from the address encoded as specified by NOTARY.
          Also generate an X400-Redirect-Recipient:" field, which
          holds the X.400 representation of the same address.  If the
          directory name is present, it should be added as a trailing
          comment in the X.400 form.

     report
          If it is MTS.Report.delivery, then set DSN.action-field to
          "delivered", and set "X400-Delivery-Time:" and
          "X400-Type-of-MTS-User:" from the information in the report.
          DSN.status field is set to "2.0.0".

          If it is MTS.Report.non-delivery, then set DSN.action-field



Kille                                                       [page 129]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          to "failure".   DSN.diagnostic-code-field is encoded
          according to the syntax EBNF.dr-diagnostic, with the
          labelled integers set from the reason and diagnotic codes.
          DSN.status-field is derived from the reason and diagnostic
          codes, as described below.

     converted-encoded-information-types
          Set X400-Converted-EITs:

     originally-intended-recipient
          Generate a DSN.final-recipient-field field, with             |
          DSN.address-type of "rfc822", and with an RFC 822 mailbox
          generated from the address encoded as specified by NOTARY.
          Also generate a DSN.original-recipient-field field, which
          holds the X.400 representation of the same address.  If the
          directory name is present, it should be added as a trailing
          comment in the X.400 form.

     supplementary-info
          Set X400-Supplementary-Info:

     redirection-history
          Set X400-Redirection-History:

     physical-forwarding-address
          Set X400-Physical-Forwarding-Address:

     recipient-certificate
          Discard

     proof-of-delivery
          Discard

     Any unknown extensions shall be discarded, irrespective of
     criticality.  All discarded extensions shall be included in a
     "X400-Discarded-DR-Extensions:" field.

          The number from the
     MTA.PerRecipientReportTransferFields.originally-specified-recipient-number
     shall be mapped to "X400-Originally-Specified-Recipient-Number:",
     in order to facilitate reverse mapping of delivery reports.

          The original message shall be included in the delivery
     status notification if it is available. The original message will



Kille                                                       [page 130]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     usually be available at the gateway, as discussed in Section 5.2.
     If the original message is available, but is not a legal message  |
     format, a dump of the ASN.1 may be included, encoded as
     application/octet-string.  This is recommended, but not required.

          Where the original message is included, it shall be encoded
     according to the MIME specifications as content type
     message/rfc822.

     5.3.8.2.  Status Code Mappings

     This section defines the mappings from X.400 diagnostic and
     status codes to the NOTARY Status field.

     C/D     X400 meaning                            DSN code        Means

     0/Any   Transfer failure (may be temporary)     4.4.0 Other net/route
     1/Any   Unable to transfer                      5.0.0 Other, unknown
     2/Any   Conversion not performed                5.6.3 Conv not supported
     3/Any   Physical rendition not performed        5.6.0 Other media error
     4/Any   Physical delivery not performed         5.1.0 Other address status
     5/Any   Restricted delivery                     5.7.1
     6/Any   Directory operation unsuccessful        5.4.3 Routing server failure
     7/Any   Deferred delivery not performed         5.3.3 Not capable























Kille                                                       [page 131]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



     1/0     Unrecognized O/R name                   5.1.1
     1/1     Ambiguous O/R name                      5.1.4
     1/2     MTS congestion                          4.3.1
     1/3     Loop detected                           5.4.6
     1/4     Recipient unavailable                   4.2.1
     1/5     Delivery time expired                   4.4.7
     1/6     Encoded information types unsupported   5.6.1 Media unsupp.
     1/7     Content too long                        5.2.3
     2/8     Conversion impractical                  5.6.3
     2/9     Conversion prohibited                   5.6.3
     1/10    Implicit conversion not subscribed      5.6.3
     1/11    Invalid arguments                       5.5.2
     1/12    Content syntax error                    5.5.2
     1/13    Size constraint violation               5.5.2
     1/14    Protocol violation                      5.5.0
     1/15    Content type not supported              5.6.1 Media unsupp.
     1/16    Too many recipients                     5.5.3
     1/17    No bilateral agreement                  5.4.4
     1/18    Unsupported critical function           5.3.3 System not capable
     2/19    Conversion with loss prohibited         5.6.2
     2/20    Line too long                           5.6.0
     2/21    Page split                              5.6.0
     2/22    Pictorial symbol loss                   5.6.2
     2/23    Punctuation symbol loss                 5.6.2
     2/24    Alphabetic character loss               5.6.2
     2/25    Multiple information loss               5.6.2
     1/26    Recipient reassignment prohibited       5.4.0 Undefined net/route
     1/27    Redirection loop detected               5.4.6
     1/28    DL expansion prohibited                 5.7.2
     1/29    No DL submit permission                 5.7.1 Delivery not authorized
     1/30    DL expansion failure                    4.2.4
     4/31    Physical rendition attrs not supported  5.6.0 Undefined media error
     4/32-45 Various physical mail stuff             5.1.0 Other address status
     1/46    Secure messaging error                  5.7.0 Other security status
     2/47    Unable to downgrade                     5.3.3 System not capable
     0/48    Unable to complete transfer             5.3.4 Message too big
     0/49    Transfer attempts limit reached         4.4.7 Delivery time expired



     5.3.8.3.  MTA Mappings

          The single SMTP recipient is constructed from                |



Kille                                                       [page 132]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     MTA.ReportTransferEnvelope.report-destination-name, using the
     mappings of Chapter 4.  Unlike with a user message, this
     information is not available at the MTS level.

     The following additional mappings are made, which results in
     fields in the outer header of the DSN.

     MTA.ReportTransferEnvelope.report-destination-name
          This is used to generate the To: field.

     MTA.ReportTransferEnvelope.identifier
          Mapped to the extended RFC 822 field "X400-MTS-Identifier:".
          It may also be used to derive a "Message-Id:" field.

     MTA.ReportTransferEnvelope.trace-information
          and

     MTA.ReportTransferEnvelope.internal-trace-information
          Mapped onto the extended RFC 822 field "X400-Received:", as
          described in Section 5.3.7.

     The following additional mappings are made, which result in per
     message fields in the DSN body part:

     MTA.PerRecipientReportTransferFields.last-trace-information
          Mapped to X400-Last-Trace:".

     MTA.PerReportTransferFields.subject-intermediate-trace-
          information Mapped to
          X400-Subject-Intermediate-Trace-Information:". These fields
          are ordered so that the most recent trace element comes
          first.

     5.3.8.4.  Example Delivery Reports

     This section contains sample delivery reports.   These are the
     same examples used in RFC 1327, and so they also illustrate the
     changes between RFC 1327 and this document.  Example Delivery
     Report 1:








Kille                                                       [page 133]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



     Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
        via Delivery Reports Channel id <27699-0@bells.cs.ucl.ac.uk>;
        Thu, 7 Feb 1991 15:48:39 +0000
     From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
     To: S.Kille@cs.ucl.ac.uk
     Subject: Delivery Report (failure) for H.Hildegard@bbn.com
     Message-Type: Delivery Report
     Date: Thu, 7 Feb 1991 15:48:39 +0000
     Message-ID: <"bells.cs.u.694:07.01.91.15.48.34"@cs.ucl.ac.uk>
     X400-Content-Identifier: Greetings.
     MIME-Version: 1.0
     Content-Type: multipart/report; report-type=delivery-status;
         boundary=boundary-1

     --boundary-1

     This report relates to your message: Greetings.

             of Thu, 7 Feb 1991 15:48:20 +0000                          |

     Your message was not delivered to
             H.Hildegard@bbn.com for the following reason:
             Bad Address
             MTA 'bbn.com' gives error message  (USER) Unknown user name in
             "H.Hildegard@bbn.com"

     The Original Message follows:


     --boundary-1
     content-type: message/delivery-status















Kille                                                       [page 134]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



     Reporting-MTA: x400;  bells.cs.ucl.ac.uk in /PRMD=uk.ac/ADMD=gold 400/C=gb/
     Arrival-Date: Thu, 7 Feb 1991 15:48:34 +0000
     DSN-Gateway: dns;  bells.cs.ucl.ac.uk
     X400-Conversion-Date: Thu, 7 Feb 1991 15:48:40 +0000
     Original-Envelope-Id:
              [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1803.665941698@UK.AC.UCL.CS>]
     X400-Content-Identifier: Greetings.
     X400-Subject-Intermediate-Trace-Information:  /PRMD=uk.ac/ADMD=gold 400/C=gb/;
              arrival Thu, 7 Feb 1991 15:48:20 +0000 action Relayed
     X400-Subject-Intermediate-Trace-Information:  /PRMD=uk.ac/ADMD=gold 400/C=gb/;
              arrival Thu, 7 Feb 1991 15:48:18 +0000 action Relayed



     Original-Recipient: rfc822; H.Hildegard@bbn.com
     Final-Recipient: x400;
       /RFC-822=H.Hildegard(a)bbn.com/OU=cs/O=ucl/PRMD=uk.ac/ADMD=gold 400/C=gb/;
     Action: failure
     Status: 5.1.1
     Diagnostic Code: x400;  Reason Unable-To-Transfer (1);
          Diagnostic Unrecognised-ORName (0)
     X400-Last-Trace: (ia5) Thu, 7 Feb 1991 15:48:18 +0000;
     X400-Originally-Specified-Recipient-Number: 1
     X400-Supplementary-Info: "MTA 'bbn.com' gives error message  (USER)
         Unknown user name in "H.Hildegard@bbn.com"";





















Kille                                                       [page 135]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



     --boundary-1
     Content-Type: message/rfc822

     Received: from glenlivet.cs.ucl.ac.uk by bells.cs.ucl.ac.uk
       with SMTP inbound id <27689-0@bells.cs.ucl.ac.uk>;
       Thu, 7 Feb 1991 15:48:21 +0000
     To: H.Hildegard@bbn.com
     Subject: Greetings.
     Phone: +44-71-380-7294
     Date: Thu, 07 Feb 91 15:48:18 +0000
     Message-ID: <1803.665941698@UK.AC.UCL.CS>
     From: Steve Kille <S.Kille@cs.ucl.ac.uk>


     Steve

     --boundary-1--                                                     |





























Kille                                                       [page 136]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



     Example Delivery Report 2:

     Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
       via Delivery Reports Channel id <27718-0@bells.cs.ucl.ac.uk>;
       Thu, 7 Feb 1991 15:49:11 +0000
     X400-Received: by mta bells.cs.ucl.ac.uk in /PRMD=uk.ac/ADMD=gold 400/C=gb/;
       Relayed; Thu, 7 Feb 1991 15:49:08 +0000
     X400-Received: by /PRMD=DGC/ADMD=GOLD 400/C=GB/; Relayed;
       Thu, 7 Feb 1991 15:48:40 +0000
     From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
     To: S.Kille@cs.ucl.ac.uk
     Subject: Delivery Report (failure) for
              j.nosuchuser@dle.cambridge.DGC.gold-400.gb
     Message-Type: Delivery Report
     Date: Thu, 7 Feb 1991 15:46:11 +0000
     Message-ID: <"DLE/910207154840Z/000"@cs.ucl.ac.uk>
     X400-Content-Identifier: A useful mess...
     MIME-Version: 1.0
     Content-Type: multipart/report; report-type=delivery-status;
         boundary=boundary-1

     --boundary-1

     This report relates to your message: A useful mess...

             of Thu, 7 Feb 1991 15:43:20 +0000                          |

     Your message was not delivered to
             j.nosuchuser@dle.cambridge.DGC.gold-400.gb
             for the following reason:
             Bad Address
             DG 21187: (CEO POA) Unknown addressee.

     The Original Message is not available












Kille                                                       [page 137]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



     --boundary-1
     content-type: message/delivery-status


     Reporting-MTA: x400; /PRMD=DGC/ADMD=GOLD 400/C=GB/
     Arrival-Date: Thu, 7 Feb 1991 15:48:40 +0000
     DSN-Gateway: dns;  bells.cs.ucl.ac.uk
     X400-Conversion-Date: Thu, 7 Feb 1991 15:49:12 +0000
     Original-Envelope-Id:
        [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1796.665941626@UK.AC.UCL.CS>]
     X400-Content-Identifier: A useful mess...



     Original-Recipient: rfc822; j.nosuchuser@dle.cambridge.DGC.gold-400.gb
     Final-Recipient: x400;
       /I=j/S=nosuchuser/OU=dle/O=cambridge/PRMD=DGC/ADMD=GOLD 400/C=GB/
     Action: failure
     Status: 5.1.1
     Diagnostic Code: x400;  Reason Unable-To-Transfer (1);
          Diagnostic Unrecognised-ORName (0)
     X400-Supplementary-Info: "DG 21187: (CEO POA) Unknown addressee."
     X400-Originally-Specified-Recipient-Number: 1

     --boundary-1--                                                     |



     5.3.9.  Probe

     This is an MTS internal issue.  Any probe shall be serviced by
     the gateway, as there is no equivalent RFC 822 functionality.
     The value of the reply is dependent on whether the gateway could
     service an MTS Message with the values specified in the probe.
     The reply shall make use of MTS.SupplementaryInformation to
     indicate that the probe was serviced by the gateway.










Kille                                                       [page 138]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Appendix A - Mappings Specific to SMTP

     This Appendix is specific to the Simple Mail Transfer  Protocol
     (RFC 821).  It describes specific changes in the context of this  |
     protocol.  When MIXER is used with SMTP, conformance to this      |
     appendix is mandatory.

     6.  Probes

     When servicing a probe, as described in section 5.3.9, use may be
     made of the SMTP VRFY command to increase the accuracy of
     information contained in the delivery report.

     7.  Long Lines

     SMTP is a text oriented protocol, and is required to support a
     line length of at least 1000 characters.   Some implementations
     do not support line lengths greater than 1000 characters.   This
     can cause problems.  Where body parts have long lines, it is
     recommended to use a MIME encoding that folds lines (quoted
     printable).

     8.  SMTP Extensions

     There are several RFCs that specify extensions to SMTP. Most of
     these are not relevant to MIXER.  The NOTARY work to support
     delivery report defines extensions which are relevant [30].  Use
     of these extensions by a MIXER gateway is optional.  If these
     extensions are used, they shall be used in the manner described
     below.                                                            |

     Editor's Note:                                                    |
          It has been proposed to make these extensions mandatory.     |
          Input is solicited.

     8.1.  SMTP Extension mapping to X.400

     Mappings are defined for the following extensions:

     NOTIFY                                                            |
          This is used to set the report and non-delivery bits of
          MTS.MTS.PerRecipientMessageSubmissionFields.originator-report-request.
          If the value is NEVER, both bits are zero.  If SUCCESS is
          present, the report bit is set.  Otherwise, the non-



Kille                                                       [page 139]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          delivery-report bit is set.  If the gateway uses the NOTIFY
          command, it shall perform this mapping in all cases.

     ORCPT                                                             |
          This may be used at the MTS level, to generate an element of
          redirection history, with the redirection date being the
          date of conversion.

     8.2.  X.400 Mapping to SMTP Extensions

     The following extensions may be used as a part of the MIXER
     mapping:

     NOTIFY                                                            |
          The report and non-delivery bits of
          MTS.MTS.PerRecipientMessageSubmissionFields.originator-report-request
          determine how this is used.   If both bits are zero, the
          parameter is NEVER.  If the report bit is set, SUCCESS is
          used.   Otherwise, FAILURE is used.  If this is done, the
          gateway shall not generate a delivery report for this
          recipient.

     ORCPT                                                             |
          If the
          MTS.perRecipientReportDeliveryFields.originally-intended-recipient-name
          is present, the ORCPT command may be used to carry this
          value.

     ENVID                                                             |
          This may be generated, with the value taken from the
          MTS.MessgeDeliveryEnvelope.message-delivery-identifer,
          encoded as EBNF.mts-msg-id.















Kille                                                       [page 140]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          Appendix B - Mapping with X.400(1984)


     This appendix defines modifications to the  mapping for use with  |
     X.400(1984).

          The X.400(1984) protocols are a proper subset of
     X.400(1988).  When mapping from X.400(1984) to RFC 822, no
     changes to this specification are needed.

          When mapping from RFC 822 to X.400(1984), no use can be made
     of 1988 specific features.   No use of such features is made at
     the MTS level.  One feature is used at the IPMS level, and this
     must be replaced by the RFC 987 approach.  All header information
     which would usually be mapped into the rfc-822-heading-list       |
     extension is mapped into a single IA5 body part, which is the     |
     first body part in the message.  This body part will start with
     the string "RFC-822-Headers:" as the first line.  The headers
     then follow this line.  This specification requires correct
     reverse mapping of this format, either from 1988 or 1984.  RFC
     822 extended headers which could be mapped into X.400(1988)
     elements, are also mapped to the body part.

          In an environment where RFC 822 is of major importance, it
     may be desirable for downgrading to consider the case where the
     message was originated in an RFC 822 system, and mapped according
     to this specification.  The rfc-822-heading-list extension may be
     mapped according to this appendix.

          When parsing std-or, the following restrictions must be
     observed:

     -    Only the 84/88 attributes identified in the table in
          Section 4.2 are present.

     -    No teletex encoding is allowed.

     If an address violates this, it should be treated as an RFC 822
     address, which will usually lead to encoding as a DDA "RFC-822".

          It is possible that null attributes may be present in an O/R
     Address.  This is not legal in 1988, except for ADMD where the
     case is explicitly described in Section 4.3.5.  Null attributes
     are deprecated (the attribute should be omitted), and should



Kille                                                       [page 141]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     therefore be unusual.  However, some systems generate them and
     rely on them.  Therefore, any null attribute shall be enoded
     using the std-or encoding (e.g., /O=/).

          If a non-Teletex Common Name (CN) is present, it should be
     mapped onto a Domain Defined Attribute "Common".  This is in line
     with RFC 1328 on X.400 1988 to 1984 downgrading [23].

          This specification defines a mapping of the Internet message
     framework to X.400.  Body part mappings are defined in RFC        |
     1494bis , which relies on X.400(88) features.   Downgrading to          [
     X.400(84) for body parts is defined in RFC 1496 (HARPOON), which        [
     shall be followed in the context of this appendix [6].                  [


































Kille                                                       [page 142]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Appendix C - RFC 822 Extensions for X.400 access                        [

     This appendix defines a number of optional mappings which may be        [
     provided to give access from RFC 822 to a number of X.400               [
     services.  These mappings are beyond the basic scope of this            [
     specification.  There has been a definite demand to use extended        [
     RFC 822 as a mechanism to access X.400, and these extensions            [
     provide access to certain features.  If this functionality is           [
     provided, this appendix shall be followed.  The following               [
     headings are defined:                                                   [

             extended-heading =
                 "Prevent-NonDelivery-Report" ":"
                 / "Generate-Delivery-Report" ":"
                 / "Alternate-Recipient" ":" prohibition
                 / "Disclose-Recipients" ":"  prohibition
                 / "Content-Return" ":" prohibition



     Prevent-NonDelivery-Report and Generate-Delivery-Report allow           [
     setting of                                                              [
     MTS.PerRecipientSubmissionFields.originator-report-request.  The        [
     setting will be the same for all recipients.                            [

          Alternate-Recipient, Disclose-Recipients, and Content-Return       [
     allow for override of the default settings for                          [
     MTS.PerMessageIndicators.                                               [



















Kille                                                       [page 143]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Appendix D - Object Identifier Assignment                               [


     The following Object Identifiers shall be used.                         [

     internet ::= OBJECT IDENTIFIER  { iso org(3) dod(6) 1 } -- from RFC 1155|
                                                                        |
     mail OBJECT IDENTIFIER ::= { internet 7 }  -- IANA assigned        |

     mixer OBJECT IDENTIFIER ::= { mail mixer(1) } -- inherited from RFC 1495|
     mixer-headings OBJECT IDENTIFIER ::= { mixer headings(1) }         |
     mixer-bodies OBJECT IDENTIFIER ::= { mixer bodies(2) }             |
                                                                        |
     id-rfc-822-field-list OBJECT IDENTIFIER ::= {mixer-headings 3}     |
     id-hex-multipart-message OBJECT IDENTIFIER ::= {mixer-headings 4}  |
     id-hex-partial-message OBJECT IDENTIFIER ::= {mixer-headings 1}    |
     id-dsn-header-list OBJECT IDENTIFIER ::= {mixer-headings 5}        |
     id-dsn-field-list OBJECT IDENTIFIER ::= {mixer-headings 6}         |
     id-mime-body-part OBJECT IDENTIFIER ::= {mixer-bodies 1}           |
     id-mime-body-part-parameters OBJECT IDENTIFIER ::= {mixer-bodies 2}|

     This object identifier for id-rfc-822-field-list is different to        [
     the one assigned in RFC 1327, which was erroneous.                      *
























Kille                                                       [page 144]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Appendix E - BNF Summary



             boolean = "TRUE" / "FALSE"


             numericstring = *DIGIT


             printablestring  = *( ps-char )
             ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                                / "," / "-" / "." / "/" / ":" / "=" / "?"
             ps-delim         = "(" / ")"
             ps-char          = ps-delim / ps-restricted-char


             ps-encoded       = *( ps-restricted-char / ps-encoded-char )
             ps-encoded-char  = "(a)"               ; (@)
                              / "(p)"               ; (%)
                              / "(b)"               ; (!)
                              / "(q)"               ; (")
                              / "(u)"               ; (_)
                              / "(l)"               ; "("
                              / "(r)"               ; ")"
                              / "(" 3DIGIT ")"


             teletex-string   = *( ps-char / t61-encoded )
             t61-encoded      = "{" 1* t61-encoded-char "}"
             t61-encoded-char = 3DIGIT


             teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]


             labelled-integer ::= [ key-string ] "(" numericstring ")"

             key-string      = *key-char
             key-char        = <a-z, A-Z, 0-9, and "-">







Kille                                                       [page 145]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



             object-identifier  ::= oid-comp object-identifier
                             | oid-comp

             oid-comp ::= [ key-string ] "(" numericstring ")"


             encoded-info    = 1#encoded-type

             encoded-type    = built-in-eit / object-identifier

             built-in-eit    = "Undefined"         ; undefined (0)
                             / "Telex"             ; tLX (1)
                             / "IA5-Text"          ; iA5Text (2)
                             / "G3-Fax"            ; g3Fax (3)
                             / "TIF0"              ; tIF0 (4)
                             / "Teletex"           ; tTX (5)
                             / "Videotex"          ; videotex (6)
                             / "Voice"             ; voice (7)
                             / "SFD"               ; sFD (8)
                             / "TIF1"              ; tIF1 (9)



             encoded-pn      = [ given "." ] *( initial "." ) surname

             given           = 2*<ps-char not including ".">

             initial         = ALPHA

             surname         = printablestring


             std-or-address  = 1*( "/" attribute "=" value ) "/"        |
             attribute       = standard-type                            |
                             / "RFC-822"                                |
                             / registered-dd-type                       |
                             / dd-key "." std-printablestring           |









Kille                                                       [page 146]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



             std-or-address-input = ( sep ) (pair) *( sep pair ) ( sep) |
             sep             = "/" / ";"                                |
             pair            = input-attribute "=" value                |
             input-attribute = attribute                                |
                             / dd-key ":" std-printablestring           |



             standard-type   = key-string

             registered-dd-type
                             = key-string dd-key          = key-string

             value           = std-printablestring

             std-printablestring
                             =  *(  std-char  /  std-pair  )  std-char
             =     <"{",     "}",     "*",     and     any     ps-char  |
                                              except  "/"  and  "="  >
             std-pair        = "$" ps-char


             global-id = std-or-address



             mta-field       = "X400-Received" ":" x400-trace
                             / "Deferred-Delivery" ":" date-time
                             / "Latest-Delivery-Time" ":" date-time



             x400-trace       = "by" md-and-mta ";"
                              [ "deferred until" date-time ";" ]
                              [ "converted" "(" encoded-info ")" ";" ]
                              [ "attempted" md-or-mta ";"  ]
                                 action-list
                                 ";" arrival-time








Kille                                                       [page 147]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



             md-and-mta       = [ "mta" mta "in" ]  global-id
             mta              = word
             arrival-time     = date-time

             md-or-mta        = "MD" global-id
                              / "MTA" mta

             Action-list      = 1#action
             action           = "Redirected"
                              / "Expanded"
                              / "Relayed"
                              / "Rerouted"


































Kille                                                       [page 148]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



             dr-user-info = dr-summary <CRLF>
                             dr-recipients <CRLF>
                             dr-content-return


             dr-content-return = "The Original Message is not available"
                  / "The Original Message follows:"

             dr-summary = "This report relates to your message:" <CRLF>
                             content-correlator <CRLF> <CRLF>
                          "of" date-time <CRLF> <CRLF>


             dr-recipients = *(dr-recipient <CRLF> <CRLF>)

             dr-recipient = dr-recip-success / dr-recip-failure

             dr-recip-success =
                             "Your message was successfully delivered to:"
                              mailbox "at" date-time


             dr-recip-failure = "Your message was not delivered to:"
                                     mailbox <CRLF>
                             "for the following reason:" *word

             report-point = [ "mta" word "in" ] global-id
             content-correlator = *word


















Kille                                                       [page 149]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



             dr-per-message-fields =
                       / "X400-Conversion-Date" ":" date-time
                       / "X400-Subject-Submision-Identifier" ":"
                                             mts-msg-id
                       / "X400-Content-Identifier" ":" printablestring
                       / "X400-Content-Type" ":" mts-content-type
                       / "X400-Original-Encoded-Information-Types" ":"
                                     encoded-info
                       / "X400-Originator-and-DL-Expansion-History" ":"
                                     dl-history
                       / "X400-Reporting-DL-Name" ":" mailbox
                       / "X400-Content-Correlator" ":" content-correlator
                       / "X400-Recipient-Info" ":" recipient-info
                       / "X400-Subject-Intermediate-Trace-Information" ":"
                                               x400-trace
                       / dr-extensions






























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RFC 1327bis
MIXER                                                DRAFT Version 2.2



             dr-per-recipient-fields =
                       / "X400-Redirect-Recipient" ":" "x400" ";" std-or
                       / "X400-Mapped-Redirect-Recipient" ":" "rfc822" ";" mailbox
                       / "X400-Converted-EITs" ":" encoded-info ";"
                       / "X400-Delivery-Time" ":" date-time
                       / "X400-Type-of-MTS-User" ":" labelled-integer
                       / "X400-Last-Trace" ":" [ encoded-info ] date-time
                       / "X400-Supplementary-Info" ":"
                             <"> printablestring <"> ";"
                       / "X400-Redirection-History" ":" redirection-comment
                       / "X400-Physical-Forwarding-Address" ":" printablestring
                       / "X400-Originally-Specified-Recipient-Number" ":"
                             integer
                       / dr-extensions

             dr-extensions = "X400-Discarded-DR-Extensions" ":"
                               1# (object-identifier / labelled-integer)


             dl-history = 1#( mailbox "(" date-time ")")

                       / "X400-Diagnostic" ":" labelled-integer
                       / "X400-Reason" ":" labelled-integer

             dr-diagnostic = "Reason" labelled-integer
                             [ ";" "Diagnostic" labelled-integer ]




















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             mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                       / "X400-Originator" ":" mailbox
                       / "X400-Recipients" ":" 1#mailbox
                       / "Original-Encoded-Information-Types" ":"
                                       encoded-info
                       / "X400-Content-Type" ":" mts-content-type
                       / "Content-Identifier" ":" printablestring
                       / "Priority" ":" priority
                       / "Originator-Return-Address" ":" 1#mailbox
                       / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                       / "Conversion" ":" prohibition
                       / "Conversion-With-Loss" ":" prohibition
                       / "Requested-Delivery-Method" ":"
                                       1*( labelled-integer )
                       / "Delivery-Date" ":" date-time
                       / "Discarded-X400-MTS-Extensions" ":"
                                    1#( object-identifier / labelled-integer )


             prohibition     = "Prohibited" / "Allowed"

             mts-msg-id       = "[" global-id ";" *text "]"

             mts-content-type = "P2" /  labelled-integer
                             / object-identifier

             priority        = "normal" / "non-urgent" / "urgent"



















Kille                                                       [page 152]


RFC 1327bis
MIXER                                                DRAFT Version 2.2



             ipn-body-format = ipn-description <CRLF>
                             [ ipn-extra-information <CRLF> ]
                             [ ipn-content-return ]

             ipn-description = ipn-receipt / ipn-non-receipt

             ipn-receipt = "Your message to:" preferred-recipient <CRLF>
                      "was received at" receipt-time <CRLF> <CRLF>
                      "This notification was generated"
                      acknowledgement-mode <CRLF>
                      "The following extra information was given:" <CRLF>
                      ipn-suppl <CRLF>

             ipn-non-receipt "Your message to:"
                     preferred-recipient <CRLF>
                     ipn-reason


             ipn-reason = ipn-discarded / ipn-auto-forwarded

             ipn-discarded = "was discarded for the following reason:"
                             discard-reason <CRLF>

             ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                             [ "The following comment was made:"
                                     auto-comment ]


             ipn-extra-information =
                      "The following information types were converted:"
                      encoded-info

             ipn-content-return = "The Original Message is not available"
                             / "The Original Message follows:"


             preferred-recipient = mailbox
             receipt-time        = date-time
             auto-comment        = printablestring
             ipn-suppl           = printablestring






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             discard-reason     = "Expired" / "Obsoleted" /
                                     "User Subscription Terminated"

             acknowledgement-mode = "Manually" / "Automatically"


             ipms-field = "Obsoletes" ":" 1#msg-id
                        / "Expiry-Date" ":" date-time
                        / "Reply-By" ":" date-time
                        / "Importance" ":" importance
                        / "Sensitivity" ":" sensitivity
                        / "Autoforwarded" ":" boolean
                        / "Incomplete-Copy" ":"
                        / "Content-Language" ":" 1#language             |
                        / "Message-Type" ":" message-type
                        / "Discarded-X400-IPMS-Extensions" ":" 1#object-identifier
                        / "Autosubmitted" ":" autosubmitted



             importance      = "low" / "normal" / "high"


             sensitivity     = "Personal" / "Private" /
                                    "Company-Confidential"

             language        = 2*ALPHA [ language-description ]
             language-description = printable-string



             message-type    = "Delivery Report"
                             / "InterPersonal Notification"
                             / "Multiple Part"



             autosubmitted   = "not-auto-submitted"
                             / "auto-generated"
                             / "auto-replied"
                             / "auto-forwarded"





Kille                                                       [page 154]


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             redirect-comment  =
                      [ "Originally To:" ] mailbox "Redirected"
                      [ "Again" ] "on" date-time
                      "To:"  redirection-reason

             redirection-reason =
                      "Recipient Assigned Alternate Recipient"
                      / "Originator Requested Alternate Recipient"
                      / "Recipient MD Assigned Alternate Recipient"
                      / "Recipient Directory Substitution Alternate Recipient"


             subject-line  = "Delivery-Report" "(" status ")"
                             [ "for" destination ]

             status        = "success" / "failure" / "success and failures"

             destination   = mailbox / "MTA" word


             extended-heading =
                 "Prevent-NonDelivery-Report" ":"
                 / "Generate-Delivery-Report" ":"
                 / "Alternate-Recipient" ":" prohibition
                 / "Disclose-Recipients" ":"  prohibition
                 / "Content-Return" ":" prohibition




     ftbp-field = "FTBP-Object-Size" ":" integer                        |
                / "FTBP-Creation-Date" ":" date-time
                / "FTBP-Modification-Date" ":" date-time
                  "FTBP-Read-Date" ":" date-time












Kille                                                       [page 155]


RFC 1327bis
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     Appendix F - Format of address mapping tables



     1.  Global Mapping Information

     The consistent operation of gateways which follow this
     specification relies of the existence of three globally defined
     mappings:

     1.   Domain Name Space -> O/R Address Space

     2.   O/R Address Space -> Domain Name Space

     3.   Domain Name Space -> O/R Address of preferred gateway

     All gateways conforming to this specification shall have access         |
     to and use these mappings.  The gateway may use standardised or
     private mechanisms to access this mapping information.

          One means of distributing this information is in three
     files.  This appendix defines a format for these files.

     2.  Mechanisms to register and to distribute Mapping Rules

          The global coordination of the mapping rules is a part of
     the DANTE
          MailFLOW Project. New mapping rules can be defined by the
     authority
          responsible for the relevant name space. The rules must be
     registered
          with a national mapping registration authority, which in
     turn passes
          them on to the central mapping registration authority.
          All the collected mapping rules are merged together into the
     globally
          coordinated mapping tables by the MailFLOW Project Team. The
     three
          tables are available from the national mapping registration
     authorities.

          To get a contact address of the mapping registration
     authority for the
          respective country or more information about the MailFLOW



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     Project
          contact:

               SWITCH
               MailFLOW Project Team
               Limmatquai 138
               8001 Zuerich
               Switzerland

               email: mailflow@mailflow.dante.net
                      S=MailFLOW;O=MailFLOW;P=DANTE;A=mailnet;C=fi;

               fax:   +41 1 268 15 68
               tel:   +41 1 268 15 20


     3.  Syntax Definitions

     An address syntax is defined, which is compatible with the syntax
     used for 822.domains.  By representing the O/R addresses as
     domains, all lookups can be mechanically implemented as domain ->
     domain mappings.  This syntax defined is initially for use in
     table format, but the syntax is defined in a manner which makes
     it suitable to be adapted for  use with the  Domain Name Service.
     This syntax allows for a general representation of O/R addresses,
     so that it can be used in other applications.  Not all attributes
     are used in the table formats defined.

          To allow the mapping of null attributes  to be represented,
     the pseudo-value "@" (not a printable string character) is used
     to indicate omission of a level in the hierarchy.  This is
     distinct from the form including the element with no value,
     although a correct X.400 implementation will interpret both in
     the same manner.

     This syntax is not intended to be handled by users.











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             dmn-or-address  = dmn-part *( "." dmn-part )
             mn-part        = dmn-attribute "$" value
             dmn-attribute  = standard-type
                             /  "~" dmn-printablestring
             value           = dmn-printablestring
                             / "@"
             dmn-printablestring =
                             = *( dmn-char / dmn-pair )
             dmn-char        = <"{", "}", "*", and any ps-char
                                                     except ".">
             dmn-pair        = "\."

     An example usage:

             ~ROLE$Big\.Chief.ADMD$ATT.C$US
             PRMD$DEC.ADMD$@.C$US

     The first example illustrates quoting of a "." and a domain
     define attribute (ROLE).  The second  example illustrates
     omission of the ADMD level. There must be a strict ordering of
     all components in this table, with the most significant
     components on the RHS.   This allows the encoding to be treated
     as a domain.



          Various further restrictions are placed on the usage of
     dmn-or-address in the address space mapping tables.

     1.   Only C, ADMD, PRMD, O, and up to four OUs may be used.

     2.   No components shall be omitted from this hierarchy, although
          the hierarchy may terminate at any level.  If the mapping is
          to an omitted component, the "@" syntax is used.

     4.  Table Lookups

     When determining a match, there are aspects which apply to all
     lookups.  Matches are always case independent. The key for all
     three  tables is a domain. The longest possible match shall be
     obtained.  Suppose the table has two entries with the following
     keys:




Kille                                                       [page 158]


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MIXER                                                DRAFT Version 2.2



             K.L
             J.K.L

     Domain "A.B.C" will not return any matches.  Domain "I.J.K.L"
     will match the entry "J.K.L:.

     5.  Domain -> O/R Address format

     The BNF is:

             domain-syntax "#" dmn-or-address "#"

     EBNF.domain-syntax is defined in Section 4.2. Note that the
     trailing "#" is used for clarity, as the dmn-or-address syntax
     might lead to values with trailing blanks.  Lines starting with
     "#" are comments.

             For example:
             AC.UK#PRMD$UK\.AC.ADMD$GOLD 400.C$GB#
             XEROX.COM#O$Xerox.ADMD$ATT.C$US#
             GMD.DE#O$@.PRMD$GMD.ADMD$DBP.C$DE#

     A domain is looked up to determine the top levels of an O/R
     Address.  Components of the domain which are not matched are used
     to build the remainder of the O/R address, as described in
     Section 4.3.4.

     6.  O/R Address -> Domain format

     The syntax of this table is:

             dmn-or-address "#" domain-syntax "#"


             For example:

             #
             # Mapping table
             #
             PRMD$UK\.AC.ADMD$GOLD 400.C$GB#AC.UK#

     The O/R Address is used to generate a domain key.  It is
     important to order the components correctly, and to fill in



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MIXER                                                DRAFT Version 2.2


     missing components in the hierarchy.  Use of this mapping is
     described in Section 4.3.2.

     7.  Domain -> O/R Address of Gateway table

     This uses the same format as the domain -> O/R address mapping.
     In this case, the restriction to only use C/ADMD/PRMD/O/OU does
     not apply.  Use of this mapping is described in Section 4.3.4. A
     domain cannot appear in this table and in the domain to O/R
     Address table.





































Kille                                                       [page 160]


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MIXER                                                DRAFT Version 2.2


     Appendix G - Conformance


     This appendix defines a number of options, which a conforming
     gateway should specify.  Conformance to this specification shall
     not be claimed if any of the mandatory features are not
     implemented.  A specification of conformance may list the service
     elements of Chapter 2, in order to be clear that full conformance
     is provied.  In particular:

     -    Formats for all fields shall be followed.

     -    The global mappings shall be supported.

     -    Formats for subject lines, delivery reports and IPNs shall
          be followed.   A system which followed the syntax, but
          translated text into a language other than english would be
          conformant.

     -    RFC 1137 shall not be followed when mapping to SMTP.

     -    All mappings of trace shall be implemented.

     -    There must be a mechanism to access all three global
          mappings.

     -    RFC 1494bis shall be followed for mapping body parts.              |

     -    When it is specified that a MIME format message is
          generated, RFC 1521 shall be followed.

     A gateway should specify:

     -    Which Interent Message Transport (822-MTS)  protocols are          |
          supported.  If SMTP is supported, Appendex A of MIXER shall
          be used.

     -    Which X.400 versions  are supported (84, 88, 92).

     -    The means by which it can access the global mappings.
          Currently, the tables of the formats define in  Appendix F
          is the only means available.

     -    The mechanism or mechanisms by which the global mapping            *



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          information is accessed.

     The following are optional parts of this specification.  A
     conforming implementation should specify which of these it
     supports.

     -    Generation of extended RFC 822 fields is mandatory.
          Optionally, they may be parsed and mapped back to X.400.  A
          gateway should should indicate if this is done, listing the
          mappings performed according to each service element of
          Chapter 2.

     -    Support for the extension mappings of Appendix C.

     -    Support for returning illegal format content in a delivery
          report

     -    Which address interpretation heuristics are supported
          (4.3.4.1)

     -    If RFC 987 generated message ids are handled in a backwards
          compatible manner (4.7.3.6)

     -    Support for FTBP.























Kille                                                       [page 162]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     Appendix H - Change History: RFC 987, 1026, 1138, 1148


     RFC 987 was the original document, and contained the key elements
     of this specification.  It was specific to X.400(1984).  RFC 1026
     specified a small number of necessary changes to RFC 987.

          RFC 1138 was based on the RFC 987 work.  It contained an
     editorial error, and was reissued a few months later as RFC 1148.
     RFC 1148 will be referred to here, as it is the document which is
     widely referred to elsewhere. The major goal of RFC 1148 was to
     upgrade RFC 987 to X.400(1988).  It did this, but did not
     obsolete RFC 987, which was recommended for use with X.400(1984).
     This appendix summarises the changes made in going from RFC 987
     to RFC 1148.

          RFC 1148 noted the following about its upgrade from RFC 987:
     Unnecessary change is usually a bad idea.  Changes on the RFC 822
     side are avoided as far as possible,  so that RFC 822 users do
     not see arbitrary differences between systems conforming to this
     specification, and those following RFC 987.  Changes on the X.400
     side are minimised, but are more  acceptable, due to the mapping
     onto a new set of services and protocols.


     1.  Introduction

     The model has shifted from a protocol based mapping to a service
     based mapping.  This has increased the generality of the
     specification, and improved the model.  This change affects the
     entire document.

          A restriction on scope has been added.

     2.  Service Elements


     -    The new service elements of X.400 are dealt with.

     -    A clear distinction is made between origination and
          reception






Kille                                                       [page 163]


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MIXER                                                DRAFT Version 2.2


     3.  Basic Mappings


     -    Add teletex support

     -    Add object identifier support

     -    Add labelled integer support

     -    Make PrintableString <-> ASCII mapping reversible

     -    The printable string mapping is aligned to the NBS mapping
          derived from RFC 987.

     4.  Addressing


     -    Support for new addressing attributes

     -    The message ID mapping is changed to not be table driven

     5.  Detailed Mappings


     -    Define extended IPM Header, and use instead of second body
          part for RFC 822 extensions

     -    Realignment of element names

     -    New syntax for reports, simplifying the header and
          introducing a mandatory body format (the RFC 987 header
          format was unusable)

     -    Drop complex autoforwarded mapping

     -    Add full mapping for IP Notifications, defining a body
          format

     -    Adopt an MTS Identifier syntax in line with the O/R Address
          syntax

     -    A new format for X400 Trace representation on the RFC 822
          side




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     6.  Appendices


     -    Move Appendix on restricted 822 mappings to a separate RFC

     -    Delete Phonenet and SMTP Appendixes









































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     Appendix I - Change History: RFC 1148 to RFC 1327



     1.  General


     -    The scope of the document was changed to cover X.400(1984),
          and so obsolete RFC 987.

     -    Changes were made to allow usage to connect RFC 822 networks
          using X.400

     -    Text was tightened to be clear about optional and mandatory
          aspects

     -    A good deal of clarification

     -    A number of minor EBNF errors

     -    Better examples are given

     -    Further X.400 upper bounds are handled correctly

     2.  Basic Mappings


     -    The encoding of object identifier is changed slightly

     3.  Addressing


     -    A global mapping of domain to preferred gateway is
          introduced.

     -    An overflow mechanism is defined for RFC 822 addresses of
          greater than 128 bytes

     -    Changes were made to improve compatibility with the PDAM on
          writing O/R Addresses.

     +         The PD and Terminal Type keywords were aligned to the
               PDAM.  It is believed that minimal use has been made of
               the RFC 1148 keywords.



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     +         P and A are allowed as alternate keys for PRMD and ADMD

     +         Where keywords are different, the PDAM keywords are
               alternatives on input.  This is mandatory.

     4.  Detailed Mappings


     -    The format of the Subject: lines is defined.

     -    Illegal use (repetition) of the heading EXTENSION is
          corrected, and a new object identifier assigned.

     -    The Delivery Report format is extensively revised in light
          of operational experience.

     -    The handling of redirects is significantly changed, as the
          previous mechanism did not work.

     5.  Appendices


     -    An SMTP appendix is added, allowing optional use of the VRFY
          command to improve probe information.

     -    Handling of JNT Mail Acknowledge-To is changed slightly.

     -    A DDA JNT-MAIL is allowed on input.

     -    The format definitions of Appendix F are explained further,
          and a third table definition added.

     -    An appendix on use with X.400(1984) is added.

     -    Optional extensions are defined to give RFC 822 access to
          further X.400 facilities.

     -    An appendix on conformance is added.









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RFC 1327bis
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     Appendix J - Change History: RFC 1327 to this Document



     1.  General

     This update is primarily for stability, and to fold in
     compatibility for MIME and to add support for the new NOTARY
     delivery status notifications.  Other general changes:

     -    Various editorial updates

     -    Minor EBNF errors

     -    Reference to mapping table support by DNS and X.500.

     -    Alignment to X.400(92)

     -    Assignment of a new object identifier

     -    Support for the EMA profile of the File Transfer Body Part.

     2.  Service Elements


     -    Support of Auto-Submitted service

     3.  Basic Mappings


     -    Comments may not be used in new headers, to remove parsing
          ambiguity

     -    RFC 1522 encoding may be used as an alternative to X.408
          downgrade, where appropriate.

     4.  Addressing


     -    Restructure of text to emphasise the global mappings

     -    Add codes and add a heuristic to align to the standard X.400
          form of writing O/R Addresses.




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     -    Improved text on ordering heuristic

     -    Leading "/" interpretation added                                   |

     -    All bar one of the address mapping heuristics made                 |
          mandatory.                                                         |

     -    Interpretation of domain defined attribute "RFC-822" made          |
          mandatory in all cases                                             |

     -    Make report request comments optional

     5.  Detailed Mappings


     -    Comments no longer maps to separate body part                      |

     -    Allow Langauges to be multi-valued

     -    Change Content-Identifier to X400-Content-Identifier, in
          order to avoid confusion with MIME.                                |

     -    Reverse mapping of MIXER defined fields made mandatory

     6.  Appendices


     -    Relaxation of restrictions on mapping 3 in Appendix F.

     -    Add linkage to HARPOON in Appendix B.

     -    RFC 1494bis added to the conformance statement of Appendix         |
          G.














Kille                                                       [page 169]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


          SECURITY CONSIDERATIONS

          Security considerations are not discussed in  this RFC.


          AUTHOR'S ADDRESS

          Steve Kille
          ISODE Consortium
          The Dome
          The Square
          Richmond
          TW9 1DT
          England

          Phone: +44-181-332-9091

          Internet EMail: S.Kille@ISODE.COM

          X.400 Email: I=S; S=Kille; O=ISODE Consortium; P=ISODE; A=Mailnet; C=FI;

          UFN:  S.Kille, ISODE Consortium, GB

























Kille                                                       [page 170]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     References


     1.

     2.   CCITT SG 5/VII, "Recommendations X.400," Message Handling
          Systems: System Model - Service Elements, October 1984.

     3.   C. Allocchio, "Mapping between X.400(1984/1988) and Mail-11
          (DECnet mail)," RFC 1405, jan 1993.

     4.   C. Allocchio, B. Cole, S. Giordano, and R. Hagens, "Using
          the Internet DNS to Distribute RFC 1327 Mail Address Mapping
          Tables," RFC 1664, aug 1994.

     5.   H.T. Alvestrand, S.E. Kille, R. Miles, M. Rose, and S.
          Thompson, "Mapping between X.400 and RFC-822 Message
          Bodies," RFC 1495, Aug 1993.

     6.   H.T. Alvestrand, J. Romaguera, and K. Jordan, "Rules for
          Downgrading Messages for X.400(88) to X.400(84) When MIME
          Consent-Types are Present in the Messages (Harpoon)," RFC
          1496, Aug 1993.

     7.   H.T. Alvestrand and S. Thompson, "Equivalences between X.400
          and RFC-822 Message Bodies," RFC 1494, Aug 1993.

     8.   H.T. Alvestrand, "Tags for the Identification of Languages,"
          RFC 17566, March 1995.

     9.   N. Borenstein and N. Freed, "MIME (Multipurpose Internet
          Mail Extensions)," RFC 1521, Sep 1993.

     10.  R.T. Braden, "Requirements for Internet Hosts -- Application
          and Support," RFC 1123, Oct 1989.

     11.  CCITT/ISO, "CCITT Recommendations X.420/ ISO IS 10021-7,"
          Message Handling Systems: Interpersonal Messaging System,
          December 1988.

     12.  CCITT/ISO, "CCITT Recommendations X.411/ ISO IS 10021-4,"
          Message Handling Systems: Message Transfer System: Abstract
          Service Definition and Procedures, December 1988.




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RFC 1327bis
MIXER                                                DRAFT Version 2.2


     13.  CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1,"
          Message Handling: System and Service Overview , December
          1988.

     14.  CCITT/ISO, "Specification of Abstract Syntax Notation One
          (ASN.1)," CCITT Recommendation X.208 / ISO IS 8824, December
          1988.

     15.  CCITT/ISO, "CCITT Recommendations X.400/ ISO IS 10021-1,"
          Message Handling: System and Service Overview , December
          1992.

     16.  D.H. Crocker, "Standard of the Format of ARPA Internet Text
          Messages," RFC 822, August 1982.

     17.  S.E. Kille, "Mapping Between X.400 and RFC 822," UK Academic
          Community Report (MG.19) / RFC 987, June 1986.

     18.  S.E. Kille, "Addendum to RFC 987," UK Academic Community
          Report (MG.23) / RFC 1026, August 1987.

     19.  S.E. Kille, "Mapping between full RFC 822 and RFC 822 with
          restricted encoding," RFC 1137, October 1989.

     20.  S.E. Kille, "Mapping Between X.400(1988) / ISO 10021 and RFC
          822," RFC 1138, October 1989.

     21.  S.E. Kille, "Mapping Between X.400(1988) / ISO 10021 and RFC
          822," RFC 1148, March 1990.

     22.  S.E. Kille, "Mapping Between X.400(1988) / ISO 10021 and RFC
          822," RFC 1327, May 1992.

     23.  S.E. Kille, "X.400 1988 to 1984 downgrading," RFC 1328, May
          1992.

     24.  S.E. Kille, "A String Encoding of Presentation Address," RFC
          1278, Nov 1992.

     25.  S.E. Kille, "A String Representation of Distinguished Name,"
          RFC 1485, Jan 1992.

     26.  S.E. Kille, "Using the OSI Directory to achieve User
          Friendly Naming," RFC 1484, Jan 1992.



Kille                                                       [page 172]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     27.  S.E. Kille, "Use of the X.500 Directory to support mapping
          between X.400 and RFC 822 Addresses," RFC in preparation,
          Sep 1994.

     28.  N. Koorland, "Message Attachmment Work Group (MAWG): MAWG
          Feasibility Project Guide," EMA Report, Version 1.3, March
          1995.

     29.  K. Moore and G. Vaudreuil, "An Extensible Message Format for
          Delivery Status Notifications," RFC Draft, May 1995.

     30.  K. Moore, "SMTP Service Extensions for Delivery Status
          Notifications," RFC Draft, May 1995.

     31.  J.B. Postel, "SIMPLE MAIL TRANSFER PROTOCOL," RFC 821,
          August 1982.

     32.  CEN/CENELEC/Information Technology/Working Group on Private
          Message Handling Systems, "FUNCTIONAL STANDARD A/3222,"
          CEN/CLC/IT/WG/PMHS N 17, October 1985.

     33.  R. Troot and S. Dorner, "Communicating Presentation
          Information in Internet Messages: The Content Dispostion
          Header," RFC 1806, June 1995.























Kille                                                       [page 173]


     1          - General .......................................  166
     2          - Basic Mappings ................................  166
     3          - Addressing ....................................  166
     4          - Detailed Mappings .............................  167
     5          - Appendices ....................................  167
     Appendix J - Change History: RFC 1327 to this Document
     ............................................................  168
     1          - General .......................................  168
     2          - Service Elements ..............................  168
     3          - Basic Mappings ................................  168
     4          - Addressing ....................................  168
     5          - Detailed Mappings .............................  169



Kille                                                         [page 3]


RFC 1327bis
MIXER                                                DRAFT Version 2.2


     6          - Appendices ....................................  169














































Kille                                                         [page 4]