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Versions: 00 01 02 03 04 05 06 07 rfc2298                               
Receipt Working Group                                       Roger Fajman
Internet Draft                             National Institutes of Health
Expires: 1 June 1997                                    26 November 1996




                    An Extensible Message Format
               for Message Disposition Notifications

                   draft-ietf-receipt-mdn-02.txt                       |


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
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Any questions, comments, and reports of defects or ambiguities in
this specification may be sent to the mailing list for the RECEIPT
working group of the IETF, using the address <receipt@cs.utk.edu>.
Requests to subscribe to the mailing list should be addressed to
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quickly be informed of any problems which might hinder inter-
operability.


Abstract

This memo defines a MIME content-type that may be used by a mail
user agent (UA) or electronic mail gateway to report the disposition
of a message after it has been sucessfully delivered to a recipient.
This content-type is intended to be machine-processable.  Additional
message headers are also defined to permit Message Disposition
Notifications (MDNs) to be requested by the sender of a message.
The purpose is to extend Internet Mail to support functionality
often found in other messaging systems, such as X.400 and the
proprietary "LAN-based" systems, and often referred to as "read
receipts," "acknowledgements," or "receipt notifications."  The
intention is to do this while respecting the privacy concerns that


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have often been expressed when such functions have been discussed in
the past.

Because many messages are sent between the Internet and other
messaging systems (such as X.400 or the proprietary "LAN-based"
systems), the MDN protocol is designed to be useful in a multi-
protocol messaging environment.  To this end, the protocol described
in this memo provides for the carriage of "foreign" addresses, in
addition to those normally used in Internet mail.  Additional
attributes may also be defined to support "tunneling" of foreign
notifications through Internet mail.


1.  Introduction

This memo defines a MIME [1] content-type for message disposition
notifications (MDNs).  An MDN can be used to notify the sender of a
message of any of several conditions that may occur after successful
delivery, such as display of the message contents, printing of the
message, deletion (without display) of the message, or the
recipient's refusal to provide MDNs.  The
"message/disposition-notification" content-type defined herein is
intended for use within the framework of the "multipart/report"
content type defined in RFC 1892 [2].

This memo defines the format of the notifications and the RFC 822
headers used to request them.


1.1 Purposes

The MDNs defined in this memo are expected to serve several pur-
poses:

(a)  Inform human beings of the disposition of messages after
     succcessful delivery, in a manner which is largely independent
     of human language;

(b)  Allow mail user agents to keep track of the disposition of
     messages sent, by associating returned MDNs with earlier
     message transmissions;

(c)  Convey disposition notification requests and disposition
     notifications between Internet Mail and "foreign" mail systems
     via a gateway;

(d)  Allow "foreign" notifications to be tunneled through a MIME-
     capable message system and back into the original messaging
     system that issued the original notification, or even to a
     third messaging system;


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(e)  Allow language-independent, yet reasonably precise, indications
     of the disposition of a message to be delivered.


1.2 Requirements

These purposes place the following constraints on the notification
protocol:

(a)  It must be readable by humans, as well as being machine-
     parsable.

(b)  It must provide enough information to allow message senders (or
     the user agents) to unambiguously associate an MDN with the
     message that was sent and the original recipient address for
     which the MDN is issued (if such information is available),
     even if the message was forwarded to another recipient address.

(c)  It must also be able to describe the disposition of a message
     independent of any particular human language or of the ter-
     minology of any particular mail system.
                                                                       |
(d)  The specification must be extensible in order to accomodate       |
     future requirements.                                              |


2.  Requesting Message Disposition Notifications                       |
                                                                       |
Message disposition notifications are requested by including a         |
Disposition-notification-to header in the message.  Further informa-   |
tion to be used by the recipient's UA in generating the MDN may be     |
provided by including Original-recipient and/or Disposition-           |
notification-options headers in the message.                           |
                                                                       |
                                                                       |
2.1 The Disposition-Notification-To Header                             |

A request that the receiving user agent issue message disposition
notifications is made by placing a Disposition-notification-to
header into the message.  The syntax of the header using the ABNF of
RFC 822 [5] is

     mdn-request-header = "Disposition-notification-to" ":" 1#mailbox  |

The address token is as specified in RFC 822 [5].

The presence of a Disposition-notification-to header in a message is
merely a request for an MDN.  The recipients' user agents are always
free to silently ignore such a request.  Alternatively, an explicit
denial of the request for information about the disposition of the


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message may be sent using the "denied" or "autodenied" disposition
in an MDN.

One and only one MDN may be issued on behalf of each particular
recipient by their user agent.  That is, once an MDN has been issued
on behalf of a recipient, no further MDNs may be issued on behalf of
that recipient, even if another disposition is performed on the
message.  However, if a message is forwarded, a "processed" or
"autoprocessed" MDN may been issued for the recipient doing the
forwarding and the recipient of the forwarded message may also cause
an MDN to be generated.

While Internet standards normally do not specify the behavior of
user interfaces, it is strongly recommended that the user agent
obtain the user's consent before sending an MDN.  This consent could
be obtained for each message through some sort of prompt or dialog
box, or globally through the user's setting of a preference.  The
user might also indicate globally that MDNs are never to be sent or
that a "denied" MDN is always sent in response to a request for an
MDN.

It is also strongly recommended that MDNs never be sent automati-
cally if the address in the Disposition-notification-to header
differs from the address in the Return-path header (see RFC 822
[5]).  In this case, confirmation from the user should be obtained,
if possible.  If obtaining consent is not possible (e.g., because
the user is not online at the time), then no MDN should be sent.
                                                                       |
It is also recommended that confirmation from the user always be       |
obtained (or no MDN sent) if there is no Return-path header in the     |
message, or if there is more than one distinct address in the          |
Disposition-notification-to header.  The comparison of the addresses   |
should be done using only the addr-spec (local-part "@" domain)        |
portion, excluding any phrase and route.  If the message contains      |
more than one Return-path header, the implementation may pick one to   |
use for the comparison, or treat the situation as a failure of the     |
comparison.                                                            |
                                                                       |
The reason for not automatically sending an MDN if the comparison      |
fails is to reduce the possibilities for mail loops and use of MDNs    |
for mail bombing.                                                      |

A message that contains a Disposition-notification-to header SHOULD
also contain a Message-ID header as specified in RFC 822 [5].  This
will permit automatic correlation of MDNs with original messages by
user agents.

If it is desired to request message disposition notifications for
some recipients and not others, two copies of the message should be
sent, one with an Disposition-notification-to header and one


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without.  The other headers of the message (To, cc, bcc, etc.) must
be the same in both copies.  The recipients in the respective
message envelopes determine for whom message disposition notifica-
tions are requested and for whom they are not.  If desired, the
Message-ID header may be the same in both copies of the message.
                                                                       |
                                                                       |
2.2 The Disposition-Notification-Options Header                        |
                                                                       |
Future extenstions to this specification may require that informa-     |
tion be supplied to the recipient's UA for additional control over     |
how and what MDNs are generated.  The Disposition-notification-        |
options header provides an extensible mechanism for such informa-      |
tion.  The syntax of this header using the ABNF of RFC 822 [5] is      |
                                                                       |
     Disposition-notification-options =                                |
          "Disposition-notification-options" ":"                       |
          disposition-notification-parameters                          |
                                                                       |
     Disposition-notification-parameters = parameter *(";" parameter)  |
                                                                       |
     parameter = attribute "=" importance "," 1#value                  |
                                                                       |
     importance = "R" / "O"                                            |
                                                                       |
The definitions of attribute and value are as in the definition of     |
the Content-type header in RFC 1521 [1].                               |
                                                                       |
An importance of R indicates that interpretation of the parameter is   |
required for proper generation of an MDN in response to this re-       |
quest.  If a UA does not understand the meaning of the parameter, it   |
MUST not generate an MDN in response to the request.  An importance    |
of O (the letter) indicates that a UA that does not understand the     |
meaning of this parameter MAY generate an MDN in response anyway,      |
ignoring the value of the parameter.                                   |
                                                                       |
No parameters are defined in this specification.  Parameters may be    |
defined in the future by later revisions or extensions to this         |
specification.  Parameter attribute names beginning with "X-" will     |
never be defined as standard names; such names are reserved for        |
experimental use.  MDN parameter names NOT beginning with "X-" MUST    |
be registered with the Internet Assigned Numbers Authority (IANA)      |
and described in an RFC.                                               |
                                                                       |
[Author's note:  is the concept of required and optional parameters    |
above adequate?  What should be done if the parameter name is          |
understood, but the values are invalid?  Do we need a disposition to   |
indicate errors in required parameters?]                               |
                                                                       |



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[Author's note:  What should we do if there is a disposition-          |
notification-options header, but no disposition-notification-to        |
header?]                                                               |

                                                                       |
2.3 The Original-Recipient Header                                      |
                                                                       |
Since electronic mail addresses may be rewritten while the message
is in transit, it is useful for the original recipient address to be
made available by the delivering MTA.  The MTA may be able to obtain
this information from the ORCPT parameter of the SMTP MAIL FROM
command, as defined in RFC 1891 [4].  If this information is avail-
able, the delivering MTA SHOULD insert an Original-recipient header
into the message.  The syntax of this header using the ABNF of RFC
822 [5] is as follows

     original-recipient-header =
          "Original-Recipient" ":" address-type ";" generic-address

The address-type and generic-address token are as as specified in
the description of the Original-recipient field in section 3.2.3.

The purpose of carrying the original recipient information and
returning it in the MDN is to permit automatic correlation of MDNs
with the original message on a per-recipient basis.


3.  Format of a Message Disposition Notification

A message disposition notification is a MIME message with a top-
level content-type of multipart/report (defined in RFC 1892 [2]).
When a multipart/report content is used to transmit an MDN:

(a)  The report-type parameter of the multipart/report content is
     "disposition-notification".

(b)  The first component of the multipart/report contains a human-
     readable explanation of the MDN, as described in RFC 1892 [2].

(c)  The second component of the multipart/report is of content-type
     message/disposition-notification, described in section 3.1 of
     this document.

(d)  If the original message or a portion of the message is to be
     returned to the sender, it appears as the third component of
     the multipart/report.

     NOTE:  For message dispostion notifications gatewayed from
     foreign systems, the headers of the original message may not be
     available.  In this case the third component of the MDN may be


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     omitted, or it may contain "simulated" RFC 822 headers which
     contain equivalent information.  In particular, it is very
     desirable to preserve the subject and date fields from the
     original message.

The MDN MUST be addressed (in both the message header and the
transport envelope) to the address from the Disposition-
notification-to header which from the original message for which the
MDN was generated.

The From field of the message header of the MDN MUST contain the
address of the person on whose behalf the message disposition
notification is being issued.

The envelope sender address (i.e., SMTP MAIL FROM) of the MDN should
be null (<>), specifying that no Delivery Status Notification
messages or other messages indicating successful or unsuccessful
delivery are to be sent in response to an MDN.

A message disposition notification MUST NOT itself request an MDN.
That is, it MUST NOT contain a Disposition-notification-to header.

The Message-ID header (if present) for an MDN MUST be different from
the Message-ID of the message for which the MDN is being issued.

A particular MDN describes the disposition of exactly one message
for exactly one recipient.  Multiple MDNs may be generated as a
result of one message submission, one per recipient.  However, due
to various circumstances, MDNs may not be generated for some
recipients for which MDNs were requested.


3.1 The message/disposition-notification content-type

The message/disposition-notification content-type is defined as
follows:

     MIME type name:                message
     MIME subtype name:             disposition-notification
     Optional parameters:           none
     Encoding considerations:       "7bit" encoding is sufficient and
                                    MUST be used to maintain readability
                                    when viewed by non-MIME mail
                                    readers.
     Security considerations:       discussed in section 5 of this memo.

The message/disposition-notification report type for use in the
multipart/report is "disposition-notification".




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The body of a message/delivery-status consists of one or more
"fields" formatted according to the ABNF of RFC 822 header "fields"
(see [5]).  Using the ABNF of RFC 822, the syntax of the
message/disposition-notification content is as follows:

     disposition-notification-content = [ reporting-ua-field CRLF ]
          [ mdn-gateway-field CRLF ]
          [ original-recipient-field CRLF ]
          final-recipient-field CRLF
          [ original-message-id-field CRLF ]
          disposition-field CRLF                                       |
          *( extension-field CRLF )


3.1.1 General conventions for fields

Since these fields are defined according to the rules of RFC 822       |
[5], the same conventions for continuation lines and comments apply.   |
Notification fields may be continued onto multiple lines by begin-
ning each additional line with a SPACE or HTAB.  Text which appears
in parentheses is considered a comment and not part of the contents
of that notification field.  Field names are case-insensitive, so
the names of notification fields may be spelled in any combination
of upper and lower case letters.  Comments in notification fields
may use the "encoded-word" construct defined in [6].


3.1.2 "*-type" subfields

Several fields consist of a "-type" subfield, followed by a semi-
colon, followed by "*text".  For these fields, the keyword used in
the address-type or MTA-type subfield indicates the expected format
of the address or MTA-name that follows.

The "-type" subfields are defined as follows:

(a)  An "address-type" specifies the format of a mailbox address.
     For example, Internet mail addresses use the "rfc822" address-
     type.

         address-type = atom

(b)  An "MTA-name-type" specifies the format of a mail transfer
     agent name.  For example, for an SMTP server on an Internet
     host, the MTA name is the domain name of that host, and the
     "dns" MTA-name-type is used.

         mta-name-type = atom




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Values for address-type and mta-name-type are case-insensitive.
Thus address-type values of "RFC822" and "rfc822" are equivalent.

The Internet Assigned Numbers Authority (IANA) will maintain a
registry of address-type and mta-name-type values, along with
descriptions of the meanings of each, or a reference to a one or
more specifications that provide such descriptions.  (The "rfc822"
address-type is defined in RFC 1891 [4].) Registration forms for
address-type and mta-name-type appear in RFC 1894 [8].

IANA will not accept registrations for any address-type name that
begins with "X-".  These type names are reserved for experimental
use.


3.1.3 Lexical tokens imported from RFC 822

The following lexical tokens, defined in RFC 822 [5], are used in
the ABNF grammar for MDNs:  addr-spec, atom, CHAR, comment, CR,
CRLF, DIGIT, LF, linear-white-space, SPACE, text.  The date-time
lexical token is defined in RFC 1123 [7].


3.2 Message/disposition-notification Fields

3.2.1 The Reporting-UA field

     reporting-ua-field = "Reporting-UA" ":" ua-name

     ua-name = *text

The Reporting-UA field is defined as follows:

A MDN describes the disposition of a message after it has been
delivered a recipient.  In all cases, the Reporting-UA is the UA
that performed the disposition described in the MDN.  This field is
optional, but recommended.  For Internet Mail user agents, it is
recommended that this field contain both the DNS name of the par-
ticular instance of the UA that generated the MDN and the name of
the product.  For example,

     Reporting-UA:  rogers-mac.dcrt.nih.gov (Foomail 97.1)


3.2.2 The MDN-Gateway field

The MDN-Gateway field indicates the name of the gateway or MTA that
translated a foreign (non-Internet) message disposition notification
into this MDN.  This field MUST appear in any MDN which was trans-



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lated by a gateway from a foreign system into MDN format, and MUST
NOT appear otherwise.

     mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name

For gateways into Internet mail, the MTA-name-type will normally be
"smtp", and the mta-name will be the Internet domain name of the
gateway.


3.2.3 Original-Recipient field

The Original-Recipient field indicates the original recipient
address as specified by the sender of the message for which the MDN
is being issued.  For Internet Mail messages the value of the
Original-Recipient field is obtained from the Original-Recipient
header from the message for which the MDN is being generated.  If
there is no Original-Recipient header in the message, then the
Original-Recipient field MUST be omitted.  If there is an Original-
Recipient header in the original message (or original recipient
information is available some other way), then the Original-
Recipient field must be supplied.

     original-recipient-field =
          "Original-Recipient" ":" address-type ";" generic-address

     generic-address = *text

The address-type field indicates the type of the original recipient
address.  If the message originated within the Internet, the
address-type field field will normally be "rfc822", and the address
will be according to the syntax specified in [5].  The value "un-
known" should be used if the Reporting UA cannot determine the type
of the original recipient address from the message envelope.  This
address is the same as that provided by the sender and can be used
to automatically correlate MDN reports with original messages on a
per recipient basis.


3.2.4 Final-Recipient field

The Final-Recipient field indicates the recipient for which the MDN
is being issued.  This field MUST be present.

The syntax of the field is as follows:

     final-recipient-field =
          "Final-Recipient" ":" address-type ";" generic-address




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The generic-address subfield of the Final-Recipient field MUST
contain the mailbox address of the recipient (from the From header)
as it was when the message was accepted by the UA.

The Final-Recipient address may differ from the address originally
provided by the sender, because it may have been transformed during
forwarding and gatewaying into an totally unrecognizable mess.
However, in the absence of the optional Original-Recipient field,
the Final-Recipient field and any returned content may be the only
information available with which to correlate the MDN with a par-
ticular message recipient.

The address-type subfield indicates the type of address expected by
the reporting MTA in that context.  Recipient addresses obtained via
SMTP will normally be of address-type "rfc822".

Since mailbox addresses (including those used in the Internet) may
be case sensitive, the case of alphabetic characters in the address
MUST be preserved.


3.2.5 Original-Message-ID field

The Original-Message-ID field indicates the message-ID of the
message for which the MDN is being issued.  It is obtained from the
Message-ID header of the message for which the MDN is issued.  This
field MUST be present if the original message contained a Message-ID
header.  The syntax of the field is

      original-message-id-field = "Original-Message-ID" ":" msg-id     |

The msg-id token is as specified in RFC 822 [5].                       |


3.2.6 Disposition field

The Disposition field indicates the action performed by the
Reporting-UA on behalf of the user.  This field MUST be present.

The syntax for the action-field is:












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     disposition-field = "Disposition" ":" disposition-value

     disposition-value =
          "acknowledged" / "autoacknowledged" /                        |
          "processed" / "autoprocessed" /                              |
          "deleted" / "autodeleted" /                                  |
          "obsoleted" / "expired" / "terminated" /                     |
          "denied" / "autodenied" /                                    |
          disposition-value-extension                                  |
                                                                       |
     disposition-value-extension = atom                                |

The disposition-value may be spelled in any combination of upper and
lower case characters.

"acknowledged"                The message has been displayed by the    |
                              UA to someone reading the recipient's    |
                              mailbox and that person explicitly       |
                              allowed the UA to send an MDN.  There    |
                              is no guarantee that the content has     |
                              been read or understood.

"autoacknowledged"            The message has been displayed by the    |
                              UA to someone reading the recipient's    |
                              mailbox and the UA sent an MDN auto-     |
                              matically.  There is no guarantee that   |
                              the content has been read or under-      |
                              stood.                                   |
                                                                       |
"processed"                   The message has been processed in some
                              manner (e.g., printed, faxed, for-
                              warded) in response to a user command,
                              without being displayed to the user.
                              The user may or may not see the
                              message later.

"autoprocessed"               The message has been processed auto-
                              matically in some manner (e.g.,
                              printed, faxed, forwarded, gatewayed)
                              in response to some user request made
                              in advance, without being displayed to
                              the user.  The user may or may not see
                              the message later.

"deleted"                     The message has been manually deleted.
                              The recipient may or may not have seen
                              the message.  The recipient might
                              "undelete" the message at a later time
                              and read the message.



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"autodeleted"                 The message has been automatically
                              deleted without being displayed to the
                              recipient.

"obsoleted"                   The message has been automatically
                              rendered obsolete by another message
                              received.  The recipient may still
                              access and read the message later.

"expired"                     The message has reached its expiration
                              date and has been automatically
                              removed from the recipient's mailbox.

"terminated"                  The recipient's mailbox has been
                              terminated and all message in it
                              automatically removed.

"denied"                      The recipient does not wish the sender
                              to be informed of the message's
                              disposition.  A UA may also siliently
                              ignore message disposition requests in
                              this situation.

"autodenied"                  The recipient does not wish the sender
                              to be informed of the message's
                              disposition and has requested that
                              this MDN be sent automatically.  A UA
                              may also siliently ignore message
                              disposition requests in this situa-
                              tion.
                                                                       |
disposition-value-extension   Additional disposition values may be     |
                              defined in the future by later revi-     |
                              sions or extensions to this specifica-   |
                              tion.  Disposition value names begin-    |
                              ning with "X-" will never be defined     |
                              as standard values; such names are       |
                              reserved for experimental use.  MDN      |
                              disposition value names NOT beginning    |
                              with "X-" MUST be registered with the    |
                              Internet Assigned Numbers Authority      |
                              (IANA) and described in an RFC.  MDNs    |
                              with disposition value names not         |
                              understood by the receiving UA MAY be    |
                              silently ignored or placed in the        |
                              user's mailbox without special inter-    |
                              pretation.  They MUST not cause any      |
                              error message to be sent to the sender   |
                              of the MDN.                              |



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It is not required that a UA be able to generate all of the possible
values of the Disposition field.

One and only one MDN may be issued on behalf of each particular
recipient by their user agent.  That is, once an MDN has been issued
on behalf of a recipient, no further MDNs may be issued on behalf of
that recipient, even if another disposition is performed on the
message.  However, if a message is forwarded, a "processed" or
"autoprocessed" MDN may been issued for the recipient doing the
forwarding and the recipient of the forwarded message may also cause
an MDN to be generated.

                                                                       |
3.3 Extension fields                                                   |

Additional MDN fields may be defined in the future by later revi-
sions or extensions to this specification.  Extension-field names
beginning with "X-" will never be defined as standard fields; such
names are reserved for experimental use.  MDN field names NOT
beginning with "X-" MUST be registered with the Internet Assigned
Numbers Authority (IANA) and described in an RFC.

Extension MDN fields may be defined for the following reasons:

(a)  To allow additional information from foreign disposition
     reports to be tunneled through Internet MDNs.  The names of
     such MDN fields should begin with an indication of the foreign
     environment name (e.g. X400-Physical-Forwarding-Address).

(b)  To allow transmission of diagnostic information which is
     specific to a particular user agent (UA).  The names of such
     MDN fields should begin with an indication of the UA implemen-
     tation which produced the MDN.  (e.g. Foomail-information).

If an UA developer does not wish to register the meanings of such
extension fields, "X-" fields may be used for this purpose.  To
avoid name collisions, the name of the UA implementation should
follow the "X-", (e.g. "X-Foomail-Log-ID").


4.  Timeline of events

The following timeline shows when various events in the processing
of a message and generation of MDNs take place:

--- User composes message
|
|-- User tells UA to send message
|
|-- UA passes message to MTA (original recipient information


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|                             passed along)
|
|-- MTA sends message to next MTA
.
.
.
|-- Final MTA receives message
|
|-- Final MTA delivers message to UA (possibily generating DSN)
|
|-- UA performs automatic processing and generates corresponding
|   MDNs (autoprocessed, autodeleted, obsoleted, expired,
|   terminated, autodenied)
|
|-- UA displays list of messages to user
|
|-- User selects a message and requests that some action be
|   performed on it.
|
|-- UA performs requested action and, with user's permission,
|   sends appropriate MDN (displayed, processed, denied).
|
|-- User possibly performs other actions on message, but no
|   further MDNs are generated


5.  Conformance and Usage Requirements

A UA or gateway conforms to this specification if it generates MDNs
according to the protocol defined in this memo.  It is not necessary
to be able to generate all of the possible values of the Disposition
field.

UAs and gateways MUST NOT generate the Original-Recipient field of
an MDN unless the mail protocols provide the address originally
specified by the sender at the time of submission.  Ordinary SMTP
does not make that guarantee, but the SMTP extension defined in RFC
1891 [4] permits such information to be carried in the envelope if
it is available.  The Original-Recipient header defined in this
document provides a way for the MTA to pass the original recipient
address to the UA.

Each sender-specified recipient address may result in more than one
MDN.  If an MDN is requested for a recipient that is forwarded to
multiple recipients of an "alias" (as defined in RFC 1891 [4],
section 7.2.7), each of the recipients may issue an MDN.

Successful distribution of a message to a mailing list exploder may
be considered final disposition of the message.  A mailing list
exploder may issue an "autoprocessed" MDN indicating that the


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message has been forwarded to the list.  In this case, the request
for MDNs is not propogated to the members of the list.  Alterna-
tively, the mailing list exploder may issue no MDN and propogate the
request for MDNs to all members of the list.  The later behavior is
not recommended for any but small, closely knit lists, as it might
cause large numbers of MDNs to be generated and may cause confiden-
tial subscribers to the list to be revealed.  It is also permissible
for the mailing list exploder to direct MDNs to itself, correlate
them, and produce a report to the original sender of the message.

This specification places no restrictions on the processing of MDNs
received by user agents or mailing lists.


6.  Security considerations

The following security considerations apply when using MDNs:


6.1 Forgery

MDNs may be forged as easily as ordinary Internet electronic mail.
User agents and automatic mail handling facilities (such as mail
distribution list exploders) that wish to make automatic use of MDNs
should take appropriate precautions to minimize the potential damage
from denial-of-service attacks.

Security threats related to forged MDNs include the sending of:

(a)  A falsified disposition notification when the indicated dis-
     position of the message has not actually ocurred,

(b)  Unsolicited MDNs


6.2 Confidentiality

Another dimension of security is confidentiality.  There may be
cases in which a message recipient does not wish the disposition of
messages addressed to him to be known or is concerned that the
sending of MDNs may reveal other confidential information (e.g.,
when the message was read).  In this situation, it is acceptable for
the UA to issue "denied" or "autodenied" MDNs or to silently ignore
requests for MDNs.

If the Disposition-notification-to header is passed on unmodified
when a message is distributed to the subscribers of a mailing list,
the subscribers to the list may be revealed to the sender of the
original message by the generation of MDNs.



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In general, any optional MDN field may be omitted if the Reporting
UA site or user determines that inclusion of the field would impose
too great a compromise of site confidentiality.  The need for such
confidentiality must be balanced against the utility of the omitted
information in MDNs.


6.3 Non-Repudiation

Within the framework of today's internet mail, the MDNs defined in
this document provide valuable information to the mail user;
however, MDNs can not be relied upon as a guarantee that a message
was or was not not seen by the recipient.  Even if MDNs are not
actively forged, they may be lost in transit.  The MDN issuing
mechanism may be bypassed in some manner by the recipient.





































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7.  Appendix - collected grammar

NOTE:  The following lexical tokens are defined in RFC 822:  addr-
spec, address, atom, CHAR, comment, CR, CRLF, DIGIT, LF, linear-
white-space, SPACE, text.  The date-time lexical token is defined in
RFC 1123 [7].

Message headers:                                                       |
                                                                       |
mdn-request-header = "Disposition-notification-to" ":" 1#mailbox       |
                                                                       |
Disposition-notification-options =                                     |
     "Disposition-notification-options" ":"                            |
     disposition-notification-parameters                               |
                                                                       |
Disposition-notification-parameters = parameter *(";" parameter)       |
                                                                       |
parameter = attribute "=" importance "," 1#value                       |
                                                                       |
importance = "R" / "O"                                                 |

original-recipient-header =
     "Original-Recipient" ":" address-type ";" generic-address

                                                                       |
Report content:                                                        |
                                                                       |
disposition-notification-content = [ reporting-ua-field CRLF ]
     [ mdn-gateway-field CRLF ]
     [ original-recipient-field CRLF ]
     final-recipient-field CRLF
     [ original-message-id-field CRLF ]                                |
     disposition-field CRLF                                            |
     *( extension-field CRLF )

address-type = atom
                                                                       |
mta-name-type = atom

reporting-ua-field = "Reporting-UA" ":" ua-name

ua-name = *text

mdn-gateway-field = "MDN-Gateway" ":" mta-name-type ";" mta-name
original-recipient-field =
     "Original-Recipient" ":" address-type ";" generic-address

generic-address = *text

final-recipient-field =


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     "Final-Recipient" ":" address-type ";" generic-address

disposition-field = "Disposition" ":" disposition-value
                                                                       |
disposition-value =                                                    |
     "acknowledged" / "autoacknowledged" /                             |
     "processed" / "autoprocessed" /                                   |
     "deleted" / "autodeleted" /                                       |
     "obsoleted" / "expired" / "terminated" /                          |
     "denied" / "autodenied"                                           |
     disposition-value-extension                                       |
                                                                       |
disposition-value-extension = atom                                     |

original-message-id-field = "Original-Message-ID" ":" msg-id           |

subscriber-address = *text

extension-field = extension-field-name ":" *text

extension-field-name = atom































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8.  Appendix - Guidelines for gatewaying MDNs

NOTE:  This section provides non-binding recommendations for the
construction of mail gateways that wish to provide semi-transparent
disposition notifications between the Internet and another
electronic mail system.  Specific MDN gateway requirements for a
particular pair of mail systems may be defined by other documents.


8.1 Gatewaying from other mail systems to MDNs

A mail gateway may issue an MDN to convey the contents of a "for-
eign" disposition notification over Internet mail.  When there are
appropriate mappings from the foreign notification elements to MDN
fields, the information may be transmitted in those MDN fields.
Additional information (such as might be needed to tunnel the
foreign notification through the Internet) may be defined in exten-
sion MDN fields.  (Such fields should be given names that identify
the foreign mail protocol, e.g. X400-* for X.400 protocol elements)

The gateway must attempt to supply reasonable values for the
Reporting-UA, Final-Recipient, and Disposition fields.  These will
normally be obtained by translating the values from the foreign
notification into their Internet-style equivalents.  However, some
loss of information is to be expected.

The sender-specified recipient address, and the original message-id,
if present in the foreign notification, should be preserved in the
Original-Recipient and Original-Message-ID fields.

The gateway should also attempt to preserve the "final" recipient
address from the foreign system.  Whenever possible, foreign
protocol elements should be encoded as meaningful printable ASCII
strings.

For MDNs produced from foreign disposition notifications, the name
of the gateway MUST appear in the MDN-Gateway field of the MDN.















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8.2 Gatewaying from MDNs to other mail systems

It may be possible to gateway MDNs from the Internet into a foreign
mail system.  The primary purpose of such gatewaying is to convey
disposition information in a form that is usable by the destination
system.  A secondary purpose is to allow "tunneling" of MDNs through
foreign mail systems, in case the MDN may be gatewayed back into the
Internet.

In general, the recipient of the MDN (i.e., the sender of the
original message) will want to know, for each recipient:  the
closest available approximation to the original recipient address,
and the disposition (displayed, printed, etc.).

If possible, the gateway should attempt to preserve the Original-
Recipient address and Original-Message-ID (if present), in the
resulting foreign disposition report.

If it is possible to tunnel an MDN through the destination environ-
ment, the gateway specification may define a means of preserving the
MDN information in the disposition reports used by that environment.































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9.  Appendix - Examples

NOTE:  These examples are provided as illustration only, and are not
considered part of the MDN protocol specification.  If an example
conflicts with the protocol definition above, the example is wrong.

Likewise, the use of *-type subfield names or extension fields in
these examples is not to be construed as a definition for those type
names or extension fields.











































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9.1 This is an MDN issued after a message has been displayed to the
user of an Internet Mail user agent.


Date: Wed, 20 Sep 1995 00:19:00 (EDT) -0400
From: Joe Recipient <Joe_Recipient@mega.edu>
Message-Id: <199509200019.12345@mega.edu>
Subject: Disposition notification
To: Jane Sender <Jane_Sender@huge.com>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=disposition-notification;
      boundary="RAA14128.773615765/mega.edu"

--RAA14128.773615765/mega.edu

The message sent on 1995 Sep 19 at 13:30:00 (EDT) -0400 to
Joe Recipient <Joe_Recipient@mega.edu> with subject "First
draft of report" has been displayed.  This is no guarantee
that the message has been read or understood.

--RAA14128.773615765/mega.edu
content-type: message/disposition-notification

Reporting-UA: joes-pc.cs.mega.edu (Foomail 97.1)
Original-Recipient: rfc822;Joe_Recipient@mega.edu
Final-Recipient: rfc822;Joe_Recipient@mega.edu
Original-Message-ID: <199509192301.12345@mega.edu>
Disposition: acknowledged                                              |

--RAA14128.773615765/mega.edu
content-type: message/rfc822

[original message goes here]

--RAA14128.773615765/mega.edu--

















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10.  Acknowledgments

This document is based on the Delivery Status Notifications document
, RFC 1894 [8], by Keith Moore and Greg Vaudreuil.  Contributions
were made by members of the IETF Receipt Working Group, including
Harald Alverstrand, Urs Eppenberger, Ned Freed, Jim Galvin, Keith
Moore, Paul Overell, Pete Resnick.                                     |
                                                                       |
[Author's note -- If you would like to be included, let me know and    |
I will add your name.]                                                 |










































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11.  References

[1]  Borenstein, N., Freed, N. "Multipurpose Internet Mail Exten-
     sions", RFC 1521, Bellcore, Innosoft, September 1993.

[2]  Vaudreuil, G. "The Multipart/Report Content Type for the
     Reporting of Mail System Administrative Messages", RFC 1892,
     Octel Network Services, January 1996.

[3]  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
     USC/Information Sciences Institute, August 1982.

[4]  Moore, K.  "SMTP Service Extension for Delivery Status
     Notifications", RFC 1891, University of Tennessee, January
     1996.

[5]  Crocker, D., "Standard for the Format of ARPA Internet Text
     Messages", STD 11, RFC 822, UDEL, August 1982.

[6]  Moore, K. "MIME (Multipurpose Internet Mail Extensions) Part
     Two:  Message Header Extensions for Non-Ascii Text", RFC 1522,
     University of Tennessee, September 1993.

[7]  Braden, R. (ed.) "Requirements for Internet Hosts - Application
     and Support", RFC 1123, October 1989.

[8]  Moore, K. and Vaudreuil, G. "An Extensible Format for Delivery
     Status Notifications, RFC 1894, University of Tennessee, Octel
     Network Services, January 1996.























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12.  Author's Address

Roger Fajman
National Institutes of Health
12 South Drive MSC 5659
Bethesda, Maryland 20892-5659
USA

Email:  raf@cu.nih.gov
Voice:  +1 301 402 4265
Fax:    +1 301 480 6241









































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