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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 5335

Network Working Group                                        J. Yeh, Ed.
Internet-Draft                                                     TWNIC
Intended status: Informational                            August 7, 2006
Expires: February 8, 2007


                    Internationalized Email Headers
                   draft-ietf-eai-utf8headers-01.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on February 8, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Full internationalization of electronic mail requires not only the
   capability to transmit non-ASCII content, to encode selected
   information in specific header fields, and to use non-ASCII
   characters in envelope addresses.  It also requires being able to
   express those addresses and information based on them in mail header
   fields.  This document specifies the use of Unicode encoded in UTF-8,
   rather than ASCII, as the base form for Internet email header field
   bodies.  This form is permitted in transmission only if authorized by



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   an SMTP extension, as specified in an associated specification.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Role of this specification . . . . . . . . . . . . . . . .  3
   2.  Background and History . . . . . . . . . . . . . . . . . . . .  3
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Pre-requirement  . . . . . . . . . . . . . . . . . . . . . . .  4
   5.  Identification of internationalized email  . . . . . . . . . .  5
   6.  Changes on Message Header Fields . . . . . . . . . . . . . . .  6
     6.1.  UTF8 Syntax  . . . . . . . . . . . . . . . . . . . . . . .  6
     6.2.  Syntax extend from RFC 2822  . . . . . . . . . . . . . . .  7
     6.3.  Change on addr-spec syntax . . . . . . . . . . . . . . . .  8
     6.4.  Trace field syntax . . . . . . . . . . . . . . . . . . . .  9
   7.  Additional issue . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Mailing list header fields . . . . . . . . . . . . . . . .  9
     7.2.  MIME headers . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   9.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 10
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   11. Edit history . . . . . . . . . . . . . . . . . . . . . . . . . 10
     11.1. draft-ietf-eai-utf8header-00 . . . . . . . . . . . . . . . 11
     11.2. draft-yeh-ima-utf8header-01  . . . . . . . . . . . . . . . 11
     11.3. draft-yeh-ima-utf8header-00  . . . . . . . . . . . . . . . 11
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     12.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 14




















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1.  Introduction

1.1.  Role of this specification

   Full internationalization of electronic mail requires several
   capabilities:

   o  The capability to transmit non-ASCII content, provided for as part
      of the basic MIME specification [RFC2045], [RFC2046].
   o  The capability to encode selected information in specific header
      fields, provided for as another part of the MIME specification
      [RFC2047].
   o  The capability to use international characters in envelope
      addresses, discussed in [EAI-overview] and specified in
      [EAI-SMTP-extension].  And, finally,
   o  The capability to express those addresses, and information related
      to and based on them, in mail header fields, defined in this
      document.

   This document specifies the use of Unicode encoded in UTF-8
   [RFC3629], rather than ASCII, as the base form for Internet email
   header fields.  This form is permitted in transmission, if authorized
   by the SMTP extension specified in [EAI-SMTP-extension].


2.  Background and History

   Mailbox names often represent the names of human users.  Many of
   these users throughout the world have names that are not normally
   represented with just the ASCII repertoire of characters, and would
   more or less like to use their real names in their mailbox names.
   These users are also likely to use non-ASCII text in their common
   names and subjects of email messages, both in what they send and what
   they receive.  This protocol specifies UTF-8 as the encoding to
   represent email header field bodies.

   The traditional format of email messages [RFC2822] only allows ASCII
   characters in the header fields of messages.  This prevents users
   from having email addresses that contain non-ASCII characters.  It
   further forces non-ASCII text in common names, comments, and in free
   text (such as in the Subject: field) to be in MIME format [RFC2047].
   This specification describes a change to the email message format
   that is connected to the SMTP message transport change described in
   the associated specifications [EAI-overview] and
   [EAI-SMTP-extension], and that allows non-ASCII characters throughout
   email header fields.  These changes affect SMTP clients, SMTP
   servers, mail user agents (MUAs), list expanders and and gateways to
   other media.



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   As specified in [EAI-SMTP-extension], an SMTP protocol extension
   "UTF8SMTP" is used to prevent the transmission of messages with UTF-8
   header fields to systems that cannot handle such messages.

   Use of this SMTP extension helps prevent against the introduction of
   such messages into message stores that might misrepresent or mangle
   such messages.  It should be noted that using an ESMTP extension does
   not prevent against transferring email messages with UTF-8 header
   fields to other systems that use the email format for messages and
   that may not be upgraded, such as the POP and IMAP protocols.  Those
   protocols also need to be changed in order to handle stored messages
   that have UTF-8 header fields.

   The objective for this protocol is to allow UTF-8 in email header
   fields.  Issues about how to handle messages that contain UTF-8
   header fields but are proposed to be delivered to systems that have
   not been upgraded to support this capability are discussed elsewhere,
   particularly in [EAI-downgrading].


3.  Terminology

   In this document, header fields are "UTF-8 header" if the bodies of
   those headers contain UTF-8 characters.

   Unless otherwise noted, all terms used here are defined in [RFC2821]
   or [RFC2822] or in [EAI-overview].

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

   This document is being discussed on the ima mailing list.  See
   https://www1.ietf.org/mailman/listinfo/ima for information about
   subscribing.  The list's archive is at
   http://www1.ietf.org/mail-archive/web/ima/index.html.


4.  Pre-requirement

   The use of UTF-8 header fields is dependent on the use of an SMTP
   extension named "UTF8SMTP".

   That protocol is defined in [EAI-SMTP-extension].  If that extension
   is not supported, UTF-8 header fields MUST NOT be transmitted by
   SMTP.

   Sending MUAs that follow this protocol MUST create all header fields



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   encoded in UTF-8.  No other direct encodings (like Big-5) are
   allowed.  Though there's nothing bad to use [RFC2047], but it is not
   recommended in this document.


5.  Identification of internationalized email

   When a SMTP client tries to send a mail to a SMTP server that does
   not support EAI, the client should know whether the message requires
   the support for EAI or not.  In addition to this, identification of
   internationalized email is also required when a message is stored and
   resent.  Checking the presence of UTF-8 characters in the header
   whenever such an identification is required may also achieve the
   goal.  However, this type of repeated processing wastes time and
   processing power of involved systems.  It is nice to have a mechanism
   (such as self-label) or some indicator to identify whether the
   message is new format(i.e.  EAI compliant) or old one (i.e.  RFC 2822
   compliant).

   To be able to do so, sending MUA MUST insert a new header field to
   identify the presence of i18n information (particularly UTF-8
   headers) in the message.  The new header specified as "UTF8SMTP", and
   elements of the header is the version number of i18n email.  The i18n
   header field syntax specified as below:

   header-content  = "UTF8SMTP:" [FWS] content-code [FWS]
                     *( ";" parameter ) CRLF
   content-code    = "UTF8" / "ASCII" / "Downgraded"
   parameter       = "Header-Language:" [FWS] Language-List
   Language-List   = Language-Tag [FWS]
                     *("," [FWS] Language-Tag [FWS])

   The Language-Tag token is the language identifier described in
   [RFC3066] (ex: zh-TW).

   [note: Thought the "parameter" token is currently used only for the
   header-language, but can be extended in future use.]

   While we can't require ordering of headers, it would be good to have
   it appear as near the top of the headers as possible.  It would also
   be good to be able to guarantee that it will be there when the
   message is dropped into a mail store.  Thus, when a i18n email is
   delivered.

   o  The "UTF8SMTP" header field MUST be inserted by the originating
      MUA.





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   o  The "UTF8SMTP" header field MUST be inserted, along with Return-
      path, by the final delivery MTA if not presented.
   o  Whenever the email need to downgrade, the content-code of the
      "UTF8SMTP" MUST change to "Downgraded", the detail of downgrade
      process will describe in [EAI-downgrading].
   o  If more than one "UTF8SMTP" header is presented, MTA SHOULD simply
      ignore any excess ones.


6.  Changes on Message Header Fields

   SMTP client can send header fields in UTF-8 format, if the UTF8SMTP
   extension advertised by SMTP server.

   This protocol does NOT change the definition of header field names.
   That is, only the bodies of header fields are allowed to have UTF-8
   characters; the rules in RFC 2822 for header names are not changed.
   To be able to do so, the header definition in RFC 2822 must extended
   to support new format.  That following ABNF is defined to substitute
   those definition in RFC 2822.

   For those tokens not referred in this section remains as the original
   definition in RFC 2822.

6.1.  UTF8 Syntax

   The use of UTF8 characters are defined as following.

   UTF8-xtra-char  =   UTF8-2 / UTF8-3 / UTF8-4

   UTF8-2          =   %xC2-DF UTF8-tail

   UTF8-3          =   %xE0 %xA0-BF UTF8-tail /
                       %xE1-EC 2(UTF8-tail) /
                       %xED %x80-9F UTF8-tail /
                       %xEE-EF 2(UTF8-tail)

   UTF8-4          =   %xF0 %x90-BF 2(UTF8-tail) /
                       %xF1-F7 3(UTF8-tail)

   UTF8-tail       =   %x80-BF

   These are taken from FRC 3629, but keep in this document for
   convenient reason.
   [Note in draft: Weather normalizing is needed or not will be place in
   here.]





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6.2.  Syntax extend from RFC 2822

   The following rules are intended to extend the corresponding rules in
   RFC 2822 to allow UTF8 characters.

   ctext   =  NO-WS-CTL /     ; all of <text> except
              %d33-39 /       ; SP, HTAB, "(", ")"
              %d42-91 /       ; and "\"
              %d93-126 /
              UTF8-xtra-char

   qtext   =       NO-WS-CTL /     ; all of <text> except
              %d33 /               ; The rest of the US-ASCII
              %d35-91 /        ; characters not including "\"
              %d93-126 /       ; or the quote character
              UTF8-xtra-char

   text    =  %d1-9 /         ; all UTF-8 characters except
              %d11-12 /       ; US-ASCII NUL, CR and LF
              %d14-127 /
              UTF8-xtra-char

   utext   =  NO-WS-CTL /     ; Non white space controls
              %d33-126 /      ; The rest of US-ASCII
              UTF8-xtra-char

   This means that all the RFC 2822 constructs that build upon these
   will permit UTF-8 characters, including comments and quoted strings.
   Besides, in order to allow UTF8 characters in <addr-spec> we have to
   change the syntax of <atext>.  However, it will also lead <mesg-id>
   to allow UTF8 characters, which is not allowed due to the limitation
   describe in Section 6.4.  So <utf8-atext> is added to meet this
   requirement.


















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   utf8-atext   =  ALPHA / DIGIT /
                   "!" / "#" /     ; Any character except
                   "$" / "%" /     ; controls, SP, and specials.
                   "&" / "'" /     ; Used for atoms
                   "*" / "+" /
                   "-" / "/" /
                   "=" / "?" /
                   "^" / "_" /
                   "`" / "{" /
                   "|" / "}" /
                   "~" /
                   UTF8-xtra-char

   utf8-atom     = [CFWS] 1*utf8-atext [CFWS]

   utf8-dot-atom = [CFWS] utf8-dot-atom-text [CFWS]

   utf8-dot-atom-text = 1*utf8-atext *("." 1*utf8-atext)

   [NOTE IN DRAFT: If any header needs to be restricted to disallow
   this, please raise the issue on the mailing list.]
   Note, however, that this does not remove any constraint on the
   character set of protocol elements; for instance, all the allowed
   values for timezone in the Date: headers are still expressed in
   ASCII.

6.3.  Change on addr-spec syntax

   In this specification, internationalized email address will be
   presented in UTF-8.  Thus, all header fields involving <mailbox>es
   may be different from traditional ones.  There might be EAI unaware
   MTAs in the mail routing path.  In that case, MTA may bounce the
   message with reply code 550, or downgrade the non-ASCII contents of
   all header bodies before continuing to send the message.  The
   downgrade process involve with a new ALT-ADDRESS parameter.  When
   downgrade occurs, the ALT-ADDRESS will be used for mail delivery
   instead of the internationalized email address, the detail is
   described in [EAI-downgrading].

   angle-addr     =  [CFWS] "<" utf8-addr-spec [alt-address] ">" [CFWS]

   utf8-addr-spec =  utf8-local-part "@" utf8-domain

   utf8-local-part=  utf8-dot-atom / quoted-string / obs-local-part

   utf8-domain    =  utf8-dot-atom / domain-literal / obs-domain

   alt-address    =  "{" [CFWS] addr-spec [CFWS] "}"



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   Below list a few possible <mailbox> representation as example.


      "DISPLAY_NAME" <ASCII@ASCII>
         ; tradition mailbox format

      "DISPLAY_NAME" <non-ASCII@non-ASCII>
         ; EAI but no ALT-ADDRESS parameter provided,
         ; message will bounce if UTF8SMTP extension is not supported

      "DISPLAY_NAME" <non-ASCII@non-ASCII {ASCII@ASCII}>
         ; UTF8SMTP with ALT-ADDRESS parameter provided,
         ; ALT-ADDRESS can be used if downgrade is necessary

6.4.  Trace field syntax

   Internationalized domain names in Received fields must be transmitted
   in punycode form.  "For" fields containing internationalized
   addresses are prohibited, since subsequent downgrading would force
   violating rules in RFC 2821 prohibiting altering existing Received
   fields.  With these two restrictions, there should be no need for
   UTF-8 information in Received fields and such information is
   prohibited to preserve the integrity of those fields.  More
   generally, UTF-8 information of any sort MUST NOT appear in Received
   fields, even in comments within those fields.


7.  Additional issue

   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
   EAI deployment.

7.1.  Mailing list header fields

   All mailing list and mail redistribution related header fields may
   need further discuss.

7.2.  MIME headers

   MIME header bodies (parameter <value> in [RFC2231]) need to allow
   UTF8 characters in conformance with this specification.


8.  Security Considerations

   If a user has a non-ASCII mailbox address and an ASCII mailbox
   address, a digital certificate that identifies that user may have



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   both addresses in the identity.  Having multiple email addresses as
   identities in a single certificate is already supported in PKIX and
   OpenPGP.

   Because UTF-8 often requires several octets to encode a single
   character, internationalized local parts may cause mail addresses to
   become longer.  As specified in RFC 2822, each line of characters
   MUST be no more 998 octets, excluding the CRLF.

   In this specification, a user could provide a ASCII alternative
   address for a non-ASCII address.  However, it is possible these two
   address going to different mailbox, or even different person.  This
   might not be the protocol problem, but user's personal choice (or
   administration policy).


9.  IANA considerations

   IANA is requested to add the "UTF8SMTP" new header to the registry
   with the entry pointing to this specification for its definition.
   For those headers that modified in this document need to have their
   registrations modified, so as to refer to the specification in
   addition to their current definitions.


10.  Acknowledgements

   This document was created by incorporating a good deal of material
   from an old Internet Draft by Paul Hoffman [Hoffman-utf8-headers].
   While many of the concepts and details have changed, the
   contributions from that draft are greatly appreciated.

   Most of the content of this document is provided by John C Klensin.
   Also some significant comments and suggestions were received from
   Charles H. Lindsey, Chris Newman, Yangwoo KO, Yoshiro YONEYA, and
   other members of the JET team and were incorporated into the
   document.  The editor is much great thanks to their contribution
   sincerely.


11.  Edit history

   This section is used for tracking the update of this document.  Will
   be removed after finalize.







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11.1.  draft-ietf-eai-utf8header-00

   1.  ABNF revise.
   2.  Terminology sync with overview document.
   3.  addr-spec change, put ALT-ADDRESS inside "<" and ">" quote with
       "{" and "}".
   4.  add IANA considerations to register the new 2822 header
       "UTF8SMTP".
   5.  add Security considerations about relation of EAI address to ALT-
       ADDRESS.

11.2.  draft-yeh-ima-utf8header-01

   1.  ABNF added.
   2.  Editrial changes.
   3.  Sent it as WG document.

11.3.  draft-yeh-ima-utf8header-00

   1.  Section re-arranged.
   2.  Remove contains are not below to this document to.


12.  References

12.1.  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.

   [EAI-SMTP-extension]
              Yao, J., Ed. and Wei. Mao, "SMTP extension for
              internationalized email address",
              draft-ietf-eai-smtpext-02.txt (work in progress),
              July 2006.

   [EAI-overview]
              Klensin, J. and Y. Ko, "Overview and Framework of
              Internationalized Email Address Delivery",
              draft-ietf-eai-framework-01.txt (work in progress),
              June 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate



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              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

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

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

   [RFC3066]  Alvestrand, H., "Tags for the Identification of
              Languages", BCP 47, RFC 3066, January 2001.

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

12.2.  Informative References

   [EAI-downgrading]
              YONEYA, Yoshiro., Ed. and Kazunori. Fujiwara, Ed.,
              "Downgrading mechanism for Internationalized eMail Address
              (IMA)", draft-ietf-eai-downgrade-01.txt (work in
              progress), June 2006.

   [Hoffman-utf8-headers]
              Hoffman, P., "SMTP Service Extensions or Transmission of
              Headers in UTF-8 Encoding",
              draft-hoffman-utf8headers-00.txt (work in progress),
              December 2003.

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

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

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








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Author's Address

   Jeff Yeh (editor)
   TWNIC
   4F-2, No. 9, Sec 2, Roosvelt Rd.
   Taipei,   100
   Taiwan

   Phone: +886 2 23411313 ext 506
   Email: jeff@twnic.net.tw









































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Full Copyright Statement

   Copyright (C) The Internet Society (2006).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
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   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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