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Versions: 00 01 02 03 04 05 rfc4952                                     
Email Address Internationalization                            J. Klensin
(EAI)
Internet-Draft                                                     Y. Ko
Intended status: Informational                                       ICU
Expires: April 15, 2007                                 October 12, 2006


           Overview and Framework for Internationalized Email
                    draft-ietf-eai-framework-02.txt

Status of this Memo

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   This Internet-Draft will expire on April 15, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Full use of electronic mail throughout the world requires that people
   be able to use their own names, written correctly in their own
   languages and scripts, as mailbox names in email addresses.  This
   document introduces a series of specifications that define mechanisms
   and protocol extensions needed to fully support internationalized
   email addresses.  These changes include an SMTP extension and
   extension of email header syntax to accommodate UTF-8 data.  The



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   document set also includes discussion of key assumptions and issues
   in deploying fully internationalized email.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Role of This Specification . . . . . . . . . . . . . . . .  3
     1.2.  Problem statement  . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Overview of the Approach . . . . . . . . . . . . . . . . . . .  6
   3.  Document Plan  . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Overview of Protocol Extensions and Changes  . . . . . . . . .  6
     4.1.  SMTP Extension for Internationalized eMail Address . . . .  7
     4.2.  Transmission of Email Header in UTF-8 Encoding . . . . . .  8
     4.3.  Downgrading Mechanism for Backward Compatibility . . . . .  8
   5.  Downgrading Before and After SMTP Transactions . . . . . . . .  9
     5.1.  Downgrading Before or During Message Submission  . . . . .  9
     5.2.  Downgrading or Other Processing After Final SMTP
           Delivery . . . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  Internationalization Considerations  . . . . . . . . . . . . . 10
   7.  Additional Issues  . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Impact on IRIs . . . . . . . . . . . . . . . . . . . . . . 10
     7.2.  Interaction with delivery notifications  . . . . . . . . . 11
     7.3.  Use of email addresses as identifiers  . . . . . . . . . . 11
     7.4.  Encoded-words, signed messages and downgrading . . . . . . 11
   8.  Experimental Targets . . . . . . . . . . . . . . . . . . . . . 12
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   12. Change History . . . . . . . . . . . . . . . . . . . . . . . . 14
     12.1. draft-klensin-ima-framework: Version 00  . . . . . . . . . 14
     12.2. draft-klensin-ima-framework: Version 01  . . . . . . . . . 14
     12.3. draft-ietf-eai-framework: Version 00 . . . . . . . . . . . 14
     12.4. draft-ietf-eai-framework: Version 01 . . . . . . . . . . . 15
     12.5. draft-ietf-eai-framework: Version 02 . . . . . . . . . . . 15
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     13.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
   Intellectual Property and Copyright Statements . . . . . . . . . . 20










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1.  Introduction

   In order to use internationalized email addresses, we need to
   internationalize both the domain part and the local part of email
   addresses.  The domain part of email addresses is already
   internationalized [RFC3490], while the local part is not.  Without
   these extensions, the mailbox name is restricted to a subset of 7-bit
   ASCII [RFC2821].  Though MIME enables the transport of non-ASCII
   data, it does not provide a mechanism for internationalized email
   address.  RFC 2047 [RFC2047] defines an encoding mechanism for some
   specific message header fields to accommodate non-ASCII data.
   However, it does not address the issue of email addresses that
   include non-ASCII characters.  Without the extensions defined here,
   or some equivalent set, the only way to incorporate non-ASCII
   characters in email addresses is to use RFC2047 coding to embed them
   in what RFC 2822 [RFC2822] calls the "display name" (known as a "name
   phrase" or by other terms elsewhere) of the relevant headers.
   Information coded into the display name is invisible in the message
   envelope and would not be considered by many to be part of the
   address at all.

1.1.  Role of This Specification

   This document presents the overview and framework for an approach to
   the next stage of email internationalization.  This new stage
   requires not only internationalization of addresses and headers, but
   also associated transport and delivery models.

   This document describes how the various elements of email
   internationalization fit together and describes the relationships
   among the various documents involved.

1.2.  Problem statement

   Though domain names are already internationalized, the
   internationalized forms are far from general adoption by ordinary
   users.  One of the reasons for this is that we do not yet have fully
   internationalized naming schemes.  Domain names are just one of the
   various names and identifiers that are required to be
   internationalized.

   Email addresses are particularly important examples in which
   internationalization of domain names alone is not sufficient.  Unless
   email addresses are presented to the user in familiar characters and
   formats, the user's perception will not be of internationalization
   and behavior that is culturally friendly.  One thing most of us have
   almost certainly learned from the experience with email usage is that
   users strongly prefer email addresses that closely resemble names or



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   initials to those involving meaningless strings of letters or
   numbers.  If the names or initials of the names in the email address
   can be expressed in the native languages and writing systems of the
   users, the Internet will be perceived as more natural, especially by
   those whose native language is not written in a subset of a Roman-
   derived script.

   Internationalization of email addresses is not merely a matter of
   changing the SMTP envelope; or of modifying the From, To, and Cc
   headers; or of permitting upgraded mail user agents (MUAs) to decode
   a special coding and respond by displaying local characters.  To be
   perceived as usable by end users, the addresses must be
   internationalized and handled consistently in all of the contexts in
   which they occur.  That requirement has far-reaching implications:
   collections of patches and workarounds are not adequate.  Even if
   they were adequate, a workaround-based approach may result in an
   assortment of implementations with different sets of patches and
   workarounds having been applied with consequent user confusion about
   what is actually usable and supported.  Instead, we need to build a
   fully internationalized email environment, focusing on permitting
   efficient communication among those who share a language or other
   community.  That, in turn, implies changes to the mail header
   environment to permit the full range of Unicode characters where that
   makes sense, an SMTP extension to permit UTF-8 [RFC3629] mail
   addressing and delivery of those extended headers, and (finally) a
   requirement for support of the 8BITMIME SMTP Extension [RFC1652] so
   that all of this can be transported through the mail system without
   having to overcome the limitation that headers do not have content-
   transfer-encodings.

1.3.  Terminology

   This document assumes a reasonable understanding of the protocols and
   terminology of the core email standards as documented in [RFC2821]
   and [RFC2822].

   Much of the description in this document depends on the abstractions
   of "Mail Transfer Agent" ("MTA") and "Mail User Agent" ("MUA").
   However, it is important to understand that those terms and the
   underlying concepts postdate the design of the Internet's email
   architecture and the application of the "protocols on the wire"
   principle to it.  That email architecture, as it has evolved, and the
   "wire" principle have prevented any strong and standardized
   distinctions about how MTAs and MUAs interact on a given origin or
   destination host (or even whether they are separate).

   In this document, an address is "all-ASCII", or just an "ASCII
   address", if every character in the address is in the ASCII character



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   repertoire [ASCII]; an address is "non-ASCII", or "an i18mail
   address", if any character is not in the ASCII character repertoire.
   Such addresses may be restricted in other ways, but those
   restrictions are not relevant here.  The term "all-ASCII" is also
   applied to other protocol elements when the distinction is important,
   with "non-ASCII" or "internationalized" as its opposite.

   The umbrella term to describe the email address internationalization
   specified by this document and its companion documents is "UTF8SMTP".
   For example, an address permitted by this specification is referred
   as a "UTF8SMTP (compliant) address".

   Please note that according to definitions given here the set of all
   "all-ASCII" addresses and the set of all "non-ASCII" addresses are
   mutually exclusive.  The set of all UTF8SMTP addresses is the union
   of these two sets.

   An "ASCII user" (i) exclusively uses email addresses that contain
   ASCII characters only, and (ii) cannot generate recipient addresses
   that contain non-ASCII characters.

   A "i18mail user" has one or more non-ASCII email addresses.  Such a
   user may have ASCII addresses too; if the user has more than one
   email address, he or she has some method to choose which address to
   use on outgoing email.  Note that under this definition, it is not
   possible to tell from the address that an email sender or recipient
   is an i18mail user.

   A "message" is sent from one user (sender) using a particular email
   address to one or more other recipient email addresses (often
   referred to just as "users" or "recipient users").

   A "mailing list" is a mechanism whereby a message may be distributed
   to multiple recipients by sending to one recipient address.  An agent
   (typically not a human being) at that single address then causes the
   message to be redistributed to the target recipients and sets the
   envelope return address of the redistributed message to a different
   error handling address from the original single recipient message.

   The pronouns "he" and "she" are used interchangeably to indicate a
   human of indeterminate gender.

   The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
   and "MAY" in this document are to be interpreted as described in RFC
   2119 [RFC2119].






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2.  Overview of the Approach

   This set of specifications changes both SMTP and the format of email
   headers to permit non-ASCII characters to be represented directly.
   Each important component of the work is described in a separate
   document.  The document set, whose members are described in the next
   section, also contains informational documents whose purpose is to
   provide implementation suggestions and guidance for the protocols.


3.  Document Plan

   In addition to this document, the following documents make up this
   specification and provide advice and context for it.

   o  SMTP extensions.  This document [I18Nemail-SMTPext] provides an
      SMTP extension for internationalized addresses, as provided for in
      RFC 2821.

   o  Email headers in UTF-8.  This document [I18Nemail-UTF8]
      essentially updates RFC 2822 to permit some information in email
      headers to be expressed directly by Unicode characters encoded in
      UTF-8 when the SMTP extension described above is used.

   o  In-transit downgrading from internationalized addressing with the
      SMTP extension and UTF-8 headers to traditional email formats and
      characters [I18Nemail-downgrade].  Downgrading either at the point
      of message origination or after the mail has successfully been
      received by a final delivery SMTP server (sometimes called an
      "MDA") involve different constraints and possibilities; see
      Section 4.3 and Section 5, below.

   o  Extensions to the IMAP protocol to support internationalized
      headers [I18Nemail-imap].

   o  Parallel extensions to the POP protocol [I18Nemail-pop].

   o  Description of internationalization changes for delivery
      notifications (DSNs) [I18Nemail-DSN].

   o  Scenarios for the use of these protocols [I18Nemail-scenarios].


4.  Overview of Protocol Extensions and Changes







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4.1.  SMTP Extension for Internationalized eMail Address

   An SMTP extension, "UTF8SMTP" is specified that

   o  Permits the use of UTF-8 strings in email addresses, both local
      parts and domain names.

   o  Permits the selective use of UTF-8 strings in email headers (see
      the next subsection).

   o  Requires that the server advertise the 8BITMIME extension
      [RFC1652] and that the client support 8-bit transmission so that
      header information can be transmitted without using a special
      content-transfer-encoding.

   o  Provides information to support downgrading mechanisms.

   Some general principles apply to this work.

   1.  Whatever encoding is used should apply to the whole address and
       be directly compatible with software used at the user interface.

   2.  An SMTP relay must

       *  Either recognize the format explicitly, agreeing to do so via
          an ESMTP option,

       *  Select and use an ASCII-only address, downgrading other
          information as needed (see Section 4.3), or

       *  Bounce the message so that the sender can make another plan.


       If the message cannot be forwarded because the next-hop system
       cannot accept the extension and insufficient information is
       available to reliably downgrade it, it MUST be bounced.

   3.  In the interest of interoperability, charsets other than UTF-8
       are prohibited.  There is no practical way to identify them
       properly with an extension similar to this without introducing
       great complexity.

   Conformance to the group of standards specified here for email
   transport and delivery requires implementation of the SMTP Extension
   specification, including recognition of the keywords associated with
   alternate addresses, and the UTF-8 Header specification.  Support for
   downgrading is not required, but, if implemented, MUST be implemented
   as specified.  Similarly, _if_ the system implements IMAP it conforms



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   to i18n IMAP spec, ditto for POP.???

4.2.  Transmission of Email Header in UTF-8 Encoding

   There are many places in MUAs or in user presentation in which email
   addresses or domain names appear.  Examples include the conventional
   From, To, or Cc header fields; Message-IDs; In-Reply-To fields that
   may contain addresses or domain names; and in message bodies.  We
   must examine all of them from an internationalization perspective.
   The user will expect to see mailbox and domain names in local
   characters, and to see them consistently.  If non-obvious encodings,
   such as protocol-specific ASCII-Compatible Encoding (ACE) variants,
   are used, the user will inevitably, if only occasionally, see them
   rather than "native" characters and will find that discomfiting or
   astonishing.  Similarly, if different codings are used for mail
   transport and message bodies, the user is particularly likely to be
   surprised, if only as a consequence of the long-established "things
   leak" principle.  The only practical way to avoid these sources of
   discomfort, in both the medium and the longer term, is to have the
   encodings used in transport be as nearly as possible the same as the
   encodings used in message headers and message bodies.

   It seems clear that the point at which email local parts are
   internationalized is the point that email headers should simply be
   shifted to a full internationalized form, presumably using UTF-8
   rather than ASCII as the base character set for other than protocol
   elements such as the header field names themselves.  The transition
   to that model includes support for address, and address-related,
   fields within the headers of legacy systems.  This is done by
   extending the encoding models of [RFC2045] and [RFC2231].  However,
   our target should be fully internationalized headers, as discussed in
   [I18Nemail-UTF8].

4.3.  Downgrading Mechanism for Backward Compatibility

   As with any use of the SMTP extension mechanism, there is always the
   possibility of a client that requires the feature encountering a
   server that does not support the required feature.  In the case of
   email address and header internationalization, the risk should be
   minimized by the fact that the selection of submission servers are
   presumably under the control of the sender's client and the selection
   of potential intermediate relays is under the control of the
   administration of the final delivery server.

   For those situations, there are basically two possibilities:

   o  Reject or bounce the message, requiring the sender to resubmit it
      with traditional-format addresses and headers.



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   o  Figure out a way to downgrade the envelope or message body in
      transit.  Especially when internationalized addresses are
      involved, downgrading will require that all-ASCII addresses be
      obtained from some source.  An optional extension parameter is
      provided as a way of transmitting an alternate address.  Downgrade
      issues and a specification are discussed in [I18Nemail-downgrade].

   The first of these two options, that of rejecting or returning the
   message to the sender MAY always be chosen.

   There is also a third case, one in which the client is I18Nemail-
   capable, the server is not, but the message does not require the
   extended capabilities.  In other words, both the addresses in the
   envelope and the entire set of headers of the message are entirely in
   ASCII (perhaps including encoded-words in the headers).  In that
   case, the client SHOULD send the message whether or not the server
   announces the capability specified here.


5.  Downgrading Before and After SMTP Transactions

   In addition to the in-transit downgrades discussed above, downgrading
   may also occur before or during initial message submission or after
   delivery to the final delivery MTA.  Because these cases have a
   different set of available information from in-transit cases, the
   constraints and opportunities may be somewhat different too.  These
   two cases are discussed in the subsections below.

5.1.  Downgrading Before or During Message Submission

   Perhaps obviously, the most convenient time to find an ASCII address
   corresponding to an internationalized address, or to convert a
   message from the internationalized form into conventional ASCII form,
   is at the originating MUA, either before the message is sent or after
   the internationalized form of the message is rejected or bounced by
   some MTA in the path to the presumed destination.  At that point, the
   user has a full range of choices available, including contacting the
   intended recipient out of band for an alternate address, consulting
   appropriate directories, arranging for translation of both addresses
   and message content into a different language, and so on.  While it
   is natural to think of message downgrading as optimally being a
   fully-automated process, we should not underestimate the capabilities
   of a user of at least moderate intelligence who wishes to communicate
   with another such user.

   In this context, one can easily imagine modifications to message
   submission servers (as described in [RFC4409]) so that they would
   perform downgrading, or perhaps even upgrading, operations, receiving



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   messages with one or more of the internationalization extensions
   discussed here and adapting the outgoing message, as needed, to
   respond to the delivery or next-hop environment it encounters.

5.2.  Downgrading or Other Processing After Final SMTP Delivery

   When an email message is received by a final delivery SMTP server, it
   is usually stored in some form.  Then it is retrieved either by
   software that reads the stored form directly or by client software
   via some email retrieval mechanisms such as POP or IMAP.

   The SMTP extension described in Section 4.1 provides protection only
   in transport.  It does not prevent MUAs and email retrieval
   mechanisms that have not been upgraded to understand
   internationalized addresses and UTF-8 headers from accessing stored
   internationalized emails.

   Since the final delivery SMTP server (or, to be more specific, its
   corresponding mail storage agent) cannot safely assume that agents
   accessing email storage will be always be capable of handling the
   extensions proposed here, it MAY either downgrade internationalized
   emails or specially identify messages that utilize these extensions,
   or both.  If this done, the final delivery SMTP server SHOULD include
   a mechanism to preserve or recover the original internationalized
   forms without information loss to support access by I18Nemail-aware
   agents.


6.  Internationalization Considerations

   This entire specification addresses issues in internationalization
   and especially the boundaries between internationalization and
   localization and between network protocols and client/user interface
   actions.


7.  Additional Issues

   This section identifies issues that are not covered as part of this
   set of specifications, but that will need to be considered as part of
   deployment of email address and header internationalization.

7.1.  Impact on IRIs

   The mailto: schema defined in [RFC2368] and discussed in IRI
   [RFC3987] may need to be modified when this work is completed and
   standardized.




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7.2.  Interaction with delivery notifications

   The advent of UTF8SMTP will make necessary consideration of the
   interaction with delivery notification mechanisms, including the SMTP
   extension for requesting delivery notifications [RFC3461], and the
   format of delivery notifications [RFC3464].  These issues are
   discussed in a forthcoming document that will update those RFCs as
   needed [I18Nemail-DSN].

7.3.  Use of email addresses as identifiers

   There are a number of places in contemporary Internet usage in which
   email addresses are used as identifiers for individuals, including as
   identifiers to web servers supporting some electronic commerce sites.
   These documents do not address those uses, but it is reasonable to
   expect that some difficulties will be encountered when
   internationalized addresses are first used in those contexts, many of
   which cannot handle the full range of addresses permitted today.

7.4.  Encoded-words, signed messages and downgrading

   One particular characteristic of the email format is its persistency:
   MUA are expected to handle messages that were originally sent decades
   ago and not just those delivered seconds ago.  As such, MUAs and mail
   filtering software will need to continue to accept and decode header
   fields that use the "encoded word" mechanism [RFC2047] to accommodate
   non-ASCII characters in some header fields.  While extensions to both
   POP3 and IMAP have been proposed to enable automatic EAI-upgrade---
   including RFC 2047 decoding---of messages by the POP3 or IMAP server,
   there are message structures and MIME content-types for which that
   cannot be done or where the change would have unacceptable side-
   effects.

   For example, message parts that are cryptographically signed using,
   e.g., S/MIME [RFC2663] or PGP [RFC3156], cannot be upgraded from RFC
   2047 form to normal UTF-8 characters without breaking the signature.
   Similarly, message parts that are encrypted encrypted) may contain,
   when decrypted, header fields that use the RFC 2047 encoding; such
   messages cannot be 'fully' upgraded without access to cryptographic
   keys.

   Similar issues may arise if signed messages are downgraded in transit
   [I18Nemail-downgrade] and then an attempt is made to upgrade them to
   the original form and then verify the signatures.  Even the very
   subtle changes that may result from algorithms to downgrade and then
   upgrade again may be sufficient to invalidate the signatures if they
   impact either the primary or MIME bodypart headers.  When signatures
   are present, downgrading must be performed with extreme care if at



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   all.


8.  Experimental Targets

   In addition to the simple question of whether the model outlined here
   can be made to work in a satisfactory way for upgraded systems and
   provide adequate protection for un-upgraded ones, we expect that
   actually working with the systems will provide answers to two
   additional questions: what restrictions such as character lists or
   normalization should be placed, if any, on the characters that are
   permitted to be used in address local-parts and how useful, in
   practice, will downgrading turn out to be given whatever restrictions
   and constraints that must be placed upon it.


9.  IANA Considerations

   This overview description and framework document does not contemplate
   any IANA registrations or other actions.  Some of the documents in
   the group have their own IANA considerations sections and
   requirements.


10.  Security Considerations

   Any expansion of permitted characters and encoding forms in email
   addresses raises some risks.  There have been discussions on so
   called "IDN-spoofing" or "IDN homograph attacks".  These attacks
   allow an attacker (or "phisher") to spoof the domain or URLs of
   businesses.  The same kind of attack is also possible on the local
   part of internationalized email addresses.  It should be noted that
   one of the proposed fixes for, e.g., domain names in URLs, does not
   work for email local parts since they are case-sensitive.  That fix
   involves forcing all elements that are displayed to be in lower-case
   and normalized.

   Since email addresses are often transcribed from business cards and
   notes on paper, they are subject to problems arising from confusable
   characters.  These problems are somewhat reduced if the domain
   associated with the mailbox is unambiguous and supports a relatively
   small number of mailboxes whose names follow local system
   conventions; they are increased with very large mail systems in which
   users can freely select their own addresses.

   The internationalization of email addresses and headers must not
   leave the Internet less secure than it is that without the required
   extensions.  The requirements and mechanisms documented in this set



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   of specifications do not, in general, raise any new security issues.
   They do require a review of issues associated with confusable
   characters -- a topic that is being explored thoroughly elsewhere
   [RFC4690] -- and, potentially, some issues with UTF-8
   canonicalization, discussed in [RFC3629].  The latter is also part of
   the subject of ongoing work discussed in [Net-Unicode].  Specific
   issues are discussed in more detail in the other documents in this
   set.  However, in particular, caution should be taken that any
   "downgrading" mechanism, or use of downgraded addresses, does not
   inappropriately assume authenticated bindings between the
   internationalized and ASCII addresses.

   The new UTF-8 header and message formats might also raise, or
   aggravate, another known issue.  If the model creates new forms of
   'invalid' or 'malformed' message, then a new email attack is created:
   in an effort to be robust, some or or most agents will accept such
   message and interpret them as if they were well-formed.  If a filter
   interprets such a message differently than then final MUA, then it
   may be possible to create a message which appears acceptable under
   the filter's interpretation but which should be rejected under the
   interpretation given it by the final MUA.  Such attacks already exist
   for existing messages and encoding layers, e.g., invalid MIME syntax,
   invalid HTML markup, and invalid coding of particular image types.

   In addition, email addresses are used in many contexts other than
   sending mail, such as for identifiers under various circumstances
   (see Section 7.3).  Each of those contexts will need to be evaluated,
   in turn, to determine whether the use of non-ASCII forms is
   appropriate and what particular issues they raise.

   This work will clearly impact any systems or mechanisms that is
   dependent on digital signatures or similar integrity protection for
   mail headers (see also the discussion in Section 7.4.  Many
   conventional uses of PGP and S/MIME are not affected since they are
   used to sign body parts but not headers.  On the other hand, the
   developing work on domain keys identified mail (DKIM [DKIM-Charter])
   will eventually need to consider this work and vice versa: while this
   experiment does not propose to address or solve the issues raised by
   DKIM and other signed header mechanisms, the issues will have to be
   coordinated and resolved eventually.


11.  Acknowledgements

   This document, and the related ones, were originally derived from
   drafts by John Klensin and the JET group [Klensin-emailaddr],
   [JET-IMA].  The work drew inspiration from discussions on the "IMAA"
   mailing list, sponsored by the Internet Mail Consortium and



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   especially from an early draft by Paul Hoffman and Adam Costello
   [Hoffman-IMAA] that attempted to define an MUA-only solution to the
   address internationalization problem.

   More recent drafts have benefited from considerable discussion within
   the IETF EAI Working Group and especially from suggestions and text
   provided by Frank Ellermann, Philip Guenther, and Kari Hurtta, and
   from extended discussions among the editors and authors of the core
   documents cited in Section 3: Harald Alvestrand, Kazunori Fujiwara,
   Chris Newman, Pete Resnick, Jiankang Yao, Jeff Yeh, and Yoshiro
   Yoneya.


12.  Change History

   This document has evolved through several titles as well as the usual
   version numbers.  The list below tries to trace that thread as well
   as changes within the substance of the document.  The first document
   of the series was posted as draft-klensin-emailaddr-i18n-00.txt in
   October 2003.

12.1.  draft-klensin-ima-framework: Version 00

   This version supercedes draft-lee-jet-ima-00 and
   draft-klensin-emailaddr-i18n-03.  It represents a major rewrite and
   change of architecture from the former and incorporates many ideas
   and some text from the latter.

12.2.  draft-klensin-ima-framework: Version 01

   o  Some clarifications of terminology (more to follow) and general
      editorial improvements.

   o  Upgrades to reflect discussions during IETF 64.

   o  Improved treatment of downgrading before and after message
      transport.

12.3.  draft-ietf-eai-framework: Version 00

   This version supercedes draft-klensin-ima-framework-01; its file name
   should represent the form to be used until the IETF email address and
   header internationalization ("EAI") work concludes.

   o  Changed "display name" terminology to be consistent with RFC 2822.
      Also clarified some other terminology issues.





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   o  Added a comment about the possible role of MessageSubmission
      servers in downgrading.

   o  Removed the "IMA" terminology, converting it to either "EAI" or
      prose.

   o  Per meeting and mailing list discussion, added conformance
      statements about bouncing if neither forwarding nor downgrading
      were possible and about implementation requirements.

   o  Updated several references.  Some documents are still tentative.

   o  Fixed many typographical errors.

12.4.  draft-ietf-eai-framework: Version 01

   o  Added comments about PGP, S/MIME, and DKIM to Security
      Considerations

   o  Rationalized terminology and included terminology from scenarios
      document.

12.5.  draft-ietf-eai-framework: Version 02

   o  Clarified comment about IRIs and MAILTO.

   o  Identified issue with S/MIME and PGP for encapsulated content.

   o  Added note about the definitive "UTF8SMTP" terminology.

   o  Removed mail exploder related discussions and reference.

   o  Adjusted some requirement levels.

   o  Removed computed ASCII address (aka ATOMIC) related discussion.

   o  Added a section about delivery notifications and created a pointer
      to a new document about them.

   o  Added a new section noting the use of email addresses as
      identifiers.

   o  Added a new section discussing implications of downgrading to
      digital signatures on messages.

   o  Many editorial revisions, corrections to references, etc.,
      including moving the references to the other documents in the
      series to "informative" -- this document does not depend on them



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      for a specification and is, itself, intended to be Informational.


13.  References

13.1.  Normative References

   [ASCII]    American National Standards Institute (formerly United
              States of America Standards Institute), "USA Code for
              Information Interchange", ANSI X3.4-1968, 1968.

              ANSI X3.4-1968 has been replaced by newer versions with
              slight modifications, but the 1968 version remains
              definitive for the Internet.

   [RFC1652]  Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
              Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
              RFC 1652, July 1994.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels'", RFC 2119, March 1997.

   [RFC2821]  Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.

   [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
              "Internationalizing Domain Names in Applications (IDNA)",
              RFC 3490, March 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

13.2.  Informative References

   [DKIM-Charter]
              IETF, "Domain Keys Identified Mail (dkim)", October 2006,
              <http://www.ietf.org/html.charters/dkim-charter.html>.

   [Hoffman-IMAA]
              Hoffman, P. and A. Costello, "Internationalizing Mail
              Addresses in Applications (IMAA)", draft-hoffman-imaa-03
              (work in progress), October 2003.

   [I18Nemail-DSN]
              Newman, C., "UTF-8 Delivery and Disposition Notification",
              draft-ietf-eai-dsn-00 (work in progress), January 2007.

              This document is under development by the WG.  The date



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              given is an estimate for a version ready for posting.

   [I18Nemail-SMTPext]
              Yao, J., Ed. and W. Mao, Ed., "SMTP extension for
              internationalized email address",
              draft-ietf-eai-smtpext-01 (work in progress), July 2006.

   [I18Nemail-UTF8]
              Yeh, J., "Internationalized Email Headers",
              draft-ietf-eai-utf8headers-01.txt (work in progress),
              August 2006.

   [I18Nemail-downgrade]
              YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading
              mechanism for Internationalized eMail Address (IMA)",
              draft-ietf-eai-downgrade-02 (work in progress),
              August 2005.

   [I18Nemail-imap]
              Resnick, P. and C. Newman, "IMAP Support for UTF-8",
              draft-ietf-eai-imap-utf8-00 (work in progress), May 2006.

   [I18Nemail-pop]
              Newman, C., "POP3 Support for UTF-8", June 2006, <http://
              www.ietf.org/internet-drafts/draft-ietf-eai-pop-00.txt>.

   [I18Nemail-scenarios]
              Alvestrand, H., "UTF-8 Mail: Scenarios",
              draft-ietf-eai-scenarios-01 (work in progress), June 2006.

   [JET-IMA]  Yao, J. and J. Yeh, "Internationalized eMail Address
              (IMA)", draft-lee-jet-ima-00 (work in progress),
              June 2005.

   [Klensin-emailaddr]
              Klensin, J., "Internationalization of Email Addresses",
              draft-klensin-emailaddr-i18n-03 (work in progress),
              July 2005.

   [Net-Unicode]
              Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", April 2006, <http://www.ietf.org/
              internet-drafts/draft-klensin-net-utf8-00.txt>.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.




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   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)
              Part Three: Message Header Extensions for Non-ASCII Text",
              RFC 2047, November 1996.

   [RFC2231]  Freed, N. and K. Moore, "MIME Parameter Value and Encoded
              Word Extensions: Character Sets, Languages, and
              Continuations", RFC 2231, November 1997.

   [RFC2368]  Hoffman, P., Masinter, L., and J. Zawinski, "The mailto
              URL scheme", RFC 2368, July 1998.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822,
              April 2001.

   [RFC3156]  Elkins, M., Del Torto, D., Levien, R., and T. Roessler,
              "MIME Security with OpenPGP", RFC 3156, August 2001.

   [RFC3461]  Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
              Extension for Delivery Status Notifications (DSNs)",
              RFC 3461, January 2003.

   [RFC3464]  Moore, K. and G. Vaudreuil, "An Extensible Message Format
              for Delivery Status Notifications", RFC 3464,
              January 2003.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4409]  Gellens, R. and J. Klensin, "Message Submission for Mail",
              RFC 4409, April 2006.

   [RFC4690]  Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
              Recommendations for Internationalized Domain Names
              (IDNs)", RFC 4690, September 2006.













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Authors' Addresses

   John C Klensin
   1770 Massachusetts Ave, #322
   Cambridge, MA  02140
   USA

   Phone: +1 617 491 5735
   Email: john-ietf@jck.com


   YangWoo Ko
   ICU
   119 Munjiro
   Yuseong-gu, Daejeon  305-732
   Republic of Korea

   Email: yw@mrko.pe.kr

































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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
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