Email Address Internationalization                               Y. Abel
(EAI)                                                              TWNIC
EAI                                                              A. Yang
Internet-Draft                                                 S. Steele                                                     TWNIC
Obsoletes: 5335 (if approved)                                  Microsoft                                  S. Steele
Updates: 2045,5321,5322                                December 08, 2010 2045,5322                                             Microsoft
(if approved)                                                 D. Crocker
Intended status: Standards Track             Brandenburg InternetWorking
Expires: June 11, July 29, 2011                                          N. Freed
                                                        January 25, 2011

                    Internationalized Email Headers


   Internet mail was originally limited to 7-bit ASCII.  Recent
   enhancements support Unicode's UTF-8 encoding in portions of a
   message.  Full internationalization of electronic mail requires not only the
   capabilities to transmit non-ASCII content, to encode selected
   additional enhancement, including support for UTF-8 in specific user-oriented
   header fields, and to use non-ASCII
   characters such as in envelope addresses.  It also requires being able to
   express those addresses and the information based on them in mail
   header To, From, and Subject fields.  This
   document specifies a variant of an enhancement to Internet mail that permits the use of Unicode encoded
   native UTF-8 support in UTF-8, rather than ASCII,
   as the base form for Internet email header field.  This form is
   permitted in transmission only if authorized by an SMTP extension, as
   specified in an associated specification.  This specification updates
   Section 6.4 and body of [RFC2045] to conform with the requirements. a message.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 11, July 29, 2011.

Copyright Notice

   Copyright (c) 2010 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Role of This Specification . . . . . .  Changes to the 8-bit clean Model<!-- (by DCrocker) --> . .  3
     1.2.  Terminology  . . . . . . . .  3
     1.2.  Relation to Other Standards . . . . . . . . . . . . . . .  3  4
   2.  Background and History . . .  Support for UTF-8 Encoding . . . . . . . . . . . . . . . . .  3
   3.  Terminology .  4
     2.1.  Message Object ABNF Changes  . . . . . . . . . . . . . . .  4
     2.2.  Normalization  . . . . . . . . .  4
   4.  Changes on Message Header Fields . . . . . . . . . . . . .  5
     2.3.  Content-Transfer-Encoding  . .  5
     4.1.  UTF-8 Syntax and Normalization . . . . . . . . . . . . . .  5
     4.2.  Changes on MIME Headers  .
   3.  Internet Message Format Enhancement  . . . . . . . . . . . . .  5
   4.  Message Labeling . . .  5
     4.3.  Syntax Extensions to RFC 5322 . . . . . . . . . . . . . .  6
     4.4.  Change on addr-spec Syntax . . . . . .  6
   5.  MIME Enhancement . . . . . . . . . .  8
     4.5.  Trace Field Syntax . . . . . . . . . . . . .  6
     5.1.  Content-Transfer-Encoding  . . . . . . .  9
     4.6.  message/global . . . . . . . . .  6
     5.2.  MIME Header Field  . . . . . . . . . . . . .  9
   5.  Security Considerations . . . . . . .  6
     5.3.  Content-Type: message/utf8-rfc822  . . . . . . . . . . . . 11  7
   6.  IANA  Security Considerations  . . . . . . . . . . . . . . . . . . . . . 11  8
   7.  Acknowledgements . .  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11  9
   8.  Edit history . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  draft-ietf-eai-rfc5335bis-00 . .  Acknowledgements . . . . . . . . . . . . . 12
     8.2.  draft-ietf-eai-rfc5335bis-01 . . . . . . . . . .  9
   9.  References . . . . . 12
     8.3.  draft-ietf-eai-rfc5335bis-02 . . . . . . . . . . . . . . . 12
     8.4.  draft-ietf-eai-rfc5335bis-03 . . . . . .  9
     9.1.  Normative References . . . . . . . . . 12
     8.5.  draft-ietf-eai-rfc5335bis-04 . . . . . . . . . .  9
     9.2.  Informative References . . . . . 12
     8.6.  draft-ietf-eai-rfc5335bis-05 . . . . . . . . . . . . . 10
   Appendix A.  Changes to support UTF-8  . . 12
     8.7.  draft-ietf-eai-rfc5335bis-06 . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14 10

1.  Introduction

1.1.  Role of This Specification

   Full internationalization of electronic

   Internet mail requires several

   o  The capability distinguishes a message from its transport and further
   divides a message between a header and a body [RFC5598].  Internet
   mail header fields contain a variety of strings that are intended to transmit non-ASCII content, provided
   be user-visible.  The range of supported characters for as part these strings
   was originally limited to a subset of [ASCII]; globalization of the basic MIME specification [RFC2045], [RFC2046].

   o  The capability to use international characters in envelope
      addresses, discussed in [I-D.ietf-eai-frmwrk-4952bis] and
   Internet requires support of the much larger set contained in [I-D.ietf-eai-rfc5336bis].

   o  The capability UTF-8
   [RFC5198].  Complex encoding alternatives to express those addresses, and information related UTF-8, as an overlay to them and based on them, in mail header fields, defined in
   the existing ASCII base, would introduce inefficiencies as well as
   opportunities for processing errors.  Native support for UTF-8
   encoding [RFC3629] is widely available among systems now used over
   the Internet.  Hence supporting this
      document. encoding directly within email
   is desired.  This document specifies a variant of an enhancement to Internet mail
   that permits the use of Unicode encoded in UTF-8 [RFC3629], encoding, rather than only ASCII, as
   the base form for Internet email header fields.

   This form specification is permitted
   in transmission, if authorized by the SMTP extension specified in
   [I-D.ietf-eai-rfc5336bis] or by other transport mechanisms capable of
   processing it.

1.2.  Relation to Other Standards

   This document updates Section 6.4 of [RFC2045].  It removes the
   blanket ban based on applying a content-transfer-encoding to all subtypes model of message/ native, end-to-end support
   for UTF-8, which uses an "8-bit clean" environment .  Support for
   carriage across legacy, 7-bit infrastructure and instead specifies for processing by
   7-bit receivers requires additional mechanisms that a composite subtype MAY
   specify whether or are not a content-transfer-encoding can be used for
   that subtype, with "cannot be used" as provided
   by this specification.

1.1.  Changes to the default. 8-bit clean Model<!-- (by DCrocker) -->

   This document also updates Section 3.4 of [RFC5322].  It Extended
   mailbox address syntax to permit UTF-8 character in Section 4.3.

   Allowing use of a content-transfer-encoding on subtypes of messages is not limited an extensive revision to transmissions the draft.  Changes include:

   o  Greatly simplified ABNF that are authorized by is much more basic and integrated.

   o  Clean separation of the SMTP
   extension specified changes in an email header [RFC5322] from
      those in [I-D.ietf-eai-rfc5336bis]. message/global (see
   Section 4.6) permits use of a content-transfer-encoding.

2.  Background and History

   Mailbox names often represent MIME header [RFC2045]

   o  Change to the names default MIME content-transfer-encoding to be 8bit

   o  Elimination of human users.  Many all discussion of
   these users throughout transport

   o  An appendix that lists the world have names derived ABNF rules that are not normally
   expressed with just inherit support
      UTF-8, due to the ASCII repertoire of characters, and would
   like changed basic rules

   Still Pending:

   o  ABF to use more or less their real names in their mailbox names.
   These users are also likely support IDN

   o  Fix "Normalization" section; I could not figure out what it needs
      to use non-ASCII text in their display
   names and subjects of email messages, both received and sent.  This
   protocol specifies UTF-8 as the encoding say.  I wasn't trying to represent email header
   field bodies. change the existing spec, but simply
      fix the writing.

   o  Review/fix MIME C-T-E details

   The traditional format goal of email messages [RFC5322] allows only 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 display names, comments, changes is to dramatically simplify the specification
   and in free
   text (such as in the "Subject:" field) software needed to be encoded (as required by
   MIME format [RFC2047]).  This specification describes support a change message with UTF8 encoding.
   Rather than specify a wide range of UTF8-specific changes to the
   email message format
   existing ABNF rules, it focuses on the few, underlying ABNF rules
   that are the basis for user-visible ASCII text.  The premise for this
   is related to simple: If the SMTP message transport
   change described is to be in the associated documents
   [I-D.ietf-eai-frmwrk-4952bis] and [I-D.ietf-eai-rfc5336bis], and that
   allows non-ASCII characters UTF-8, then it is in most email header fields.  These
   changes affect SMTP clients, SMTP servers, mail user agents (MUAs),
   list expanders, gateways to other media, and all other processes that
   parse UTF-8.
   Subtle or handle email messages.

   As specified in [I-D.ietf-eai-rfc5336bis], an SMTP protocol extension
   "UTF8SMTP" is used to prevent the transmission of messages with UTF-8
   header fields to systems complex rules that cannot handle such messages.

   Use of this SMTP extension helps prevent selectively add UTF-8 are not worth the
   effort, once the introduction of such
   messages into message stores that might misinterpret, improperly
   display, or mangle such messages.  It should be noted that using an
   ESMTP extension does not prevent transferring email messages with
   UTF-8 header fields to other systems that use has already entered into the email format for
   messages and that may not be upgraded, such as unextended POP and
   IMAP servers.  Changes to these protocols to handle UTF-8 header
   fields are addressed in [I-D.ietf-eai-rfc5721bis] and
   [I-D.ietf-eai-5378bis]. realm of UTF-8.

   The objective for this protocol is to allow UTF-8 in email header

3.  Terminology

   A plain ASCII string question, then, is full compatible with [RFC5321] and [RFC5322].
   In whether this document, non-ASCII strings are UTF-8 strings if they are change has planted some
   landmines, such as in Trace header which contain at least one <UTF8-non-ascii>.

   Unless otherwise noted, all terms used here are defined in [RFC5321],
   [RFC5322], [I-D.ietf-eai-frmwrk-4952bis], or
   [I-D.ietf-eai-rfc5336bis]. fields?

1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

4.  Changes on Message Header Fields

   SMTP clients can send header fields

   Syntax descriptions use Augmented BNF (ABNF) [RFC5234].

   Basic terms for this specification include:

      ASCII:   An encoding of Control Characters and Basic Latin that
         occupies 7-bits, per [ASCII].  Such a string is fully
         compatible with email as specified in [RFC5322].

      UTF-8:   An encoding of Unicode in 8-bit bytes, per [RFC3629].

2.  Support for UTF-8 format, if the UTF8SMTP
   extension Encoding

2.1.  Message Object ABNF Changes

   Internet Mail that conforms to this specification is advertised by classed as
   supporting UTF-8.  However, UTF-8 characters within the SMTP server or is permitted by other
   transport mechanisms.

   This protocol does NOT change ASCII range
   retain the [RFC5322] rules restrictions defined for defining header
   field names.  The bodies of header fields are allowed original, legacy, Latin-only
   email.  Therefore, ABNF enhancements to contain include UTF-8 characters, but incrementally
   add the header field names themselves must contain
   only ASCII characters.

   To permit non-ASCII portions of UTF-8 to that established base of

   UTF-8 characters in field values, the header definition in
   [RFC5322] is extended to support the new format.  The following ABNF
   is defined to substitute those definitions in [RFC5322].

   The syntax rules not covered in this section remain as defined in

4.1.  UTF-8 Syntax and Normalization

   UTF-8 characters can be defined in terms of octets using are defined by using the following ABNF [RFC5234], taken from


   UTF8-enhancement  =   UTF8-2 / UTF8-3 / UTF8-4

   UTF8-2            =   <See Section 4 of RFC3629>

   UTF8-3            =   <See Section 4 of RFC3629>

   UTF8-4            =   <See Section 4 of RFC3629>

2.2.  Normalization

   See [RFC5198] for a discussion of normalization; the use of
   normalization normalization.  A normalized form
   [NFC] is RECOMMENDED.  Actually, if one is going
   to do internationalization properly, one of the most often-cited
   goals is to permit people to spell their names correctly.  Since many
   mailbox local parts reflect personal names, that principle applies as
   well.  And NFKC is not recommended because it may MAY be used.  However [NFC] can lose information that is needed
   to correctly spell some names in unusual circumstances.

4.2.  Changes on MIME Headers

   This specification updates Section 6.4 of [RFC2045].  [RFC2045]
   prohibits applying a content-transfer-encoding to any subtypes of

2.3.  Content-Transfer-Encoding

   This specification relaxes the rule -- it allows newly
   defined MIME types to permit content-transfer-encoding, and it allows
   content-transfer-encoding for message/global (see Section 4.6).

   Background: Normally, transfer of message/global will be done in
   8-bit-clean channels, and body parts will have "identity" encodings,
   that is, no decoding is necessary.  In the case where a message
   containing based on a message/global is downgraded from 8-bit to 7-bit as
   described in [RFC1652], requirement for an encoding may be applied to the message; if
   the message travels multiple times between "8-bit clean"
   infrastructure.  Support for UTF-8 semantics within a 7-bit
   environment and an
   environment implementing UTF8SMTP, multiple levels of encoding may
   occur.  This is expected to be rarely seen in practice, and the
   potential complexity of other ways of dealing with the issue are
   thought to be larger than the complexity of allowing nested encodings
   where necessary.

4.3.  Syntax Extensions to RFC 5322

   The following rules are intended to extend the corresponding rules in
   [RFC5322] in order to allow UTF-8 characters.

   FWS     =  <see Section 3.2.2 of RFC 5322>

   CFWS    =  <see Section 3.2.2 of RFC 5322>

   ctext   =/  UTF8-non-ascii
               ; Extending ctext in RFC 5322, Section 3.2.2
   comment =   "(" *([FWS] uCcontent) [FWS] ")"

   word    =   uAtom / uQuoted-String

   This means that all the [RFC5322] constructs requires translation conventions that build upon these
   will permit UTF-8 characters, including comments and quoted strings.
   We do are not change the syntax specified
   here.  Consequently a Content-Transfer-Encoding value of <atext> in order to allow UTF-8
   characters in <addr-spec>.  This would also allow UTF-8 characters in
   <message-id>, which 7-bit is not allowed due to the limitation described in
   Section 4.5.  Instead, <uAtext> is added to meet this requirement.

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

   uQuoted-Pair   = ("\" (VCHAR / WSP / UTF8-non-ascii )) / obs-qp

   VCHAR          = <See appendix B.1 of RFC 5234>

   WSP            = <See appendix B.1 of RFC 5234>

   obs-qp         = <See Section 4.1 of RFC 5322>

   uQcontent      = uQtext / uQuoted-Pair

   DQUOTE         = <See appendix B.1 of RFC 5234>

   uCcontent      = ctext / uQuoted-Pair / comment

   uQtext         = qtext / UTF8-non-ascii

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

   uAtom          = [CFWS] 1*uAtext [CFWS]

   uDot-Atom      = [CFWS] uDot-Atom-text [CFWS]

   uDot-Atom-text = 1*uAtext *("." 1*uAtext)

   To allow the use of UTF-8 in a Content-Description header field
   [RFC2045], the following syntax is used:

   description    = "Content-Description" ":" *uText
                   ; Replace description in RFC 2045, Section 8

   The <uText> syntax is extended above to allow UTF-8 in all
   <description> header fields.

   Note, however, this does not remove any constraint on the character
   set of protocol elements; for instance, all the allowed values for
   timezone in the "Date:" header fields are still expressed in ASCII.
   And also, none of this revised syntax changes what is allowed in a
   <msg-id>, which will still remain in pure ASCII.

4.4.  Change on addr-spec Syntax

   Internationalized email addresses are represented in UTF-8.  Thus,
   all header fields containing <mailbox>es are updated from [RFC5321]
   Section 4.1.2 to permit UTF-8 addresses.

   mailbox        = name-addr / addr-spec / uAddr-Spec
                    ; Replace mailbox in RFC 5322, Section 3.4

   angle-addr     =/ [CFWS] "<" uAddr-Spec ">" [CFWS]
                    ; Extending angle-addr in RFC 5322, Section 3.4

   uAddr-Spec     = uLocal-Part "@" uDomain

   uLocal-Part    = uDot-Atom / uQuoted-String / obs-local-part
                    ; Replace Local-Part in RFC 5322, Section 3.4.1

   uQuoted-String = [CFWS] DQUOTE *([FWS] uQcontent) [FWS] DQUOTE [CFWS]

   obs-local-part = <See Section 4.4 of RFC 5322>
   uDomain        = uDot-Atom / domain-literal / obs-domain

   domain-literal = <See Section 3.4.1 of RFC 5322>

   Below are a few examples of possible <mailbox> representations.

      ; traditional mailbox format

      "DISPLAY_NAME" <non-ASCII@non-ASCII>
      ; message will be rejected if UTF8SMTP extension is not supported

      ; without DISPLAY_NAME and quoted string
      ; message will be rejected if UTF8SMTP extension is not supported

4.5.  Trace Field Syntax

   The 'uFor' clause in "Received:" fields has been allowed the use of
   internationalized addresses in "For" fields.  It described in
   [I-D.ietf-eai-rfc5336bis], Section 3.6.3.

   The "Return-path" designates the address to which messages indicating
   non-delivery or other mail system failures are to be sent.  Thus, the
   header that is augmented to carry labeled as containing UTF-8.

3.  Internet Message Format Enhancement

   This section specifies UTF-8 addresses (see enhancements for the revised syntax header of <angle-addr> an
   Internet Mail message, as defined in [RFC5322].

   ABNF used in Section 4.4 of this document). section is taken from that specification and the
   ABNF specification.

   This will not
   break specification retains the rule of trace [RFC5322] rules for defining header
   field integrity, because names.  The bodies of header fields are allowed to contain
   UTF-8 characters, but the header field is
   added at names themselves must contain
   only ASCII characters.

   The following rules extend the last MTA and described corresponding rules in [RFC5321].

   The <received-token> on "Received:" field ( described [RFC5322] and
   [RFC5234] in Section
   3.6.7 of [RFC5322]) syntax is augmented order to allow additional UTF-8 email address
   in characters.

   VCHAR   =/  UTF8-non-ascii

   ctext   =/  UTF8-enhancement

   atext   =/  UTF8-enhancement

   qtext   =/  UTF8-enhancement

   TENTATIVE (DCrocker):
   text    =/  UTF8-enhancement
                  ; note that this upgrades the "For" field. <angle-addr> is augmented body to include UTF-8 email
   address.  In order

   {{ how to allow add IDN to this? }}
   domain  =   dot-atom / domain-literal / obs-domain

   This means that all the [RFC5322] constructs that build upon these
   will permit UTF-8 email addresses in an <addr-spec>,
   <uAddr-Spec> is added characters, including comments and quoted strings.

      <field-name>   [RFC5322] has the rule <field-name> which specifies
         permissible names for user-defined header fields.  The current
         specification defines no changes to that rule.

      <msg-id>   This ABNF enables Message-ID strings to <received-token>.

   received-token =/ uAddr-Spec

4.6.  message/global

   Internationalized messages MUST only be transmitted as authorized by
   [I-D.ietf-eai-rfc5336bis] or within full UTF-8.
         However the specification directs that Message-ID strings
         SHOULD be restricted to ASCII.

4.  Message Labeling

   For clarity and convenience, a non-SMTP environment which
   supports these messages.  A message is SHOULD contain an explicit
   label indicating the character base it uses.  This section defines a "message/global message",
   new header field for this label:
   fields         =/ msg-character
   msg-character  = "MSG-Char:" ( "ASCII" / "UTF-8" ) CRLF

5.  MIME Enhancement

5.1.  Content-Transfer-Encoding

   The default "Content-Transfer-Encoding: is 8BIT" and is assumed if

   o  it
   the Content-Transfer-Encoding header field is not present.

5.2.  MIME Header Field

   MIME contains at least one header field that is intended for user
   display, namely Content-Description.  This section specifies UTF-8
   enhancements to MIME header values fields, as specified defined in this document, or

   o  it contains UTF-8 values [RFC2045].  ABNF
   rules used in this section is taken from that specification and the headers fields of body parts.
   ABNF specification.

   The enhanced ABNF rules are:
   text    =/ UTF8-non-ascii

5.3.  Content-Type: message/utf8-rfc822

   The type message/global message/utf-rfc822 is similar to message/rfc822, except that message/rfc822.  However it
   specifies that a message can contain UTF-8 characters in the headers
   of the message or body parts.  If this type is sent to a 7-bit-only
   system, it has to be encoded in MIME [RFC2045].  (Note that a system
   compliant with MIME that doesn't recognize message/global SHOULD
   treat it as "application/octet-stream" are interpreted as described in Section 5.2.4
   of [RFC2046].) UTF-8 rather than being
   limited to ASCII.

   Type name:  message

   Subtype name:  global  utf8-rfc822

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  Any content-transfer-encoding is permitted.
      The 8-bit or binary content-transfer-encodings are recommended
      where permitted.

   Security considerations:  See Section 5. 6.

   Interoperability considerations:  The media type provides
      functionality similar to the message/rfc822 content type for email
      messages with international email headers.  When there is a need
      to embed or return such content in another message, there is
      generally an option to use this media type and leave the content
      unchanged or down-convert the content to message/rfc822.  Both of
      these choices will interoperate with the installed base, but with
      different properties.  Systems unaware of internationalized
      headers will typically treat a message/global message/utf8-rfc822 body part as an
      unknown attachment, while they will understand the structure of a
      message/rfc822.  However, systems that understand message/global message/
      utf8-rfc822 will provide functionality superior to the result of a down-
      down-conversion to message/rfc822.  The most interoperable choice
      depends on the deployed software.

   Published specification:  RFC XXXX

   Applications that use this media type:  SMTP servers and email
      clients that support multipart/report generation or parsing.
      Email clients which forward messages with international headers as

   Additional information:

   Magic number(s):  none

   File extension(s):  The extension ".u8msg" is suggested.

   Macintosh file type code(s):  A uniform type identifier (UTI) of
      "public.utf8-email-message" is suggested.  This conforms to
      "public.message" and "public.composite-content", but does not
      necessarily conform to "public.utf8-plain-text".

   Person & email address to contact for further information:  See the
      Author's Address section of this document.

   Intended usage:  COMMON

   Restrictions on usage:  This is a structured media type which embeds
      other MIME media types.  The 8-bit or binary content-transfer-
      encoding SHOULD be used unless this media type is sent over a
      7-bit-only transport.

   Author:  See the Author's Address section of this document.

   Change controller:  IETF Standards Process


6.  Security Considerations

   If a user has a non-ASCII mailbox address in UTF-8 and an ASCII a mailbox
   address, address in
   ASCII, a digital certificate that identifies that user may might have
   both addresses in the identity.  Having multiple email addresses as
   identities in a single certificate is already supported in PKIX
   (Public Key Infrastructure for X.509 Certificates) [RFC5280] and
   OpenPGP [RFC3156].

   Because UTF-8 often requires several octets to encode a single
   character, internationalized local parts and header value may cause
   mail addresses to become longer.  As specified in [RFC5322], each
   line of characters MUST be no more 998 octets, excluding the CRLF.
   On the other hand, MDA (Mail Delivery Agent) processes that parse,
   store, or handle email addresses or local parts must take extra care
   not to overflow buffers, truncate addresses, or exceed storage
   allotments.  Also, they must take care, when comparing, to use the
   entire lengths of the addresses.

   The security impact of UTF-8 headers on email signature systems such
   as Domain Keys Identified Mail (DKIM), S/MIME, and OpenPGP is
   discussed in [I-D.ietf-eai-frmwrk-4952bis], [I-D.eai-frmwrk-4952bis], Section 14.


7.  IANA Considerations

   IANA is requested to update the registration of the message/global message/
   utf8-rfc822 MIME type using the registration form contained in
   Section 4.6.

7. 5.3.

8.  Acknowledgements

   This document incorporates many ideas first described in Internet-
   Draft form by Paul Hoffman, although many details have changed from
   that earlier work.

   The author especially thanks Jeff Yeh for his efforts and
   contributions on editing previous versions.

   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, Kari Hurtta, Pete Resnick, Alexey Melnikov, Chris
   Newman, Yangwoo Ko, Yoshiro Yoneya, and other members of the JET team
   (Joint Engineering Team) and were incorporated into the document.
   The editor sincerely thanks them for their contributions.

8.  Edit history

   [[RFC Editor: please remove this section before publishing.]]

8.1.  draft-ietf-eai-rfc5335bis-00

   1.  Applied Errata suggested by Alfred Hoenes.

   2.  Adjust [RFC2821] and [RFC2822] to [RFC5321] and [RFC5322].

   3.  Abrogate <alt-address> in ABNF of <angle-addr>.

   4.  Revoke [RFC5504] from this document.

   5.  Upgrade some references from I-Ds to RFC.

8.2.  draft-ietf-eai-rfc5335bis-01

   1.  Author name revised.

8.3.  draft-ietf-eai-rfc5335bis-02

   1.  ABNF revised.

8.4.  draft-ietf-eai-rfc5335bis-03

   1.  Fix typos

   2.  ABNF revised

   3.  Improve sentence

8.5.  draft-ietf-eai-rfc5335bis-04

   1.  improve sentences and ABNF revised based on AD and Co-chairs

8.6.  draft-ietf-eai-rfc5335bis-05

   1.  ABNF revised in Section 4.4 based on AD comments

8.7.  draft-ietf-eai-rfc5335bis-06

   1.  ABNF revised

   2.  improve Section 6

9.  References

9.1.  Normative References

   [I-D.ietf-eai-5378bis]         Resnick, P., Newman, C., and S. Shen,
                                  "IMAP Support

   [ASCII]                   "Coded Character Set -- 7-bit American
                             Standard Code for UTF-8",
                                  draft-ietf-eai-5378bis-00 (work in
                                  progress), November 2010.

   [I-D.ietf-eai-frmwrk-4952bis] Information Interchange",
                             ANSI X3.4, 1986.

   [I-D.eai-frmwrk-4952bis]  Klensin, J. and Y. Ko, "Overview and
                             Framework for Internationalized Email",
                             draft-ietf-eai-frmwrk-4952bis-10 (work in
                             progress), September 2010.

   [I-D.ietf-eai-rfc5336bis]      Yao, J. and W. MAO, "SMTP Extension
                                  for Internationalized Email Address",
                                  draft-ietf-eai-rfc5336bis-07 (work in
                                  progress), December 2010.

   [I-D.ietf-eai-rfc5721bis]      Gellens, R., Newman, C., Yao, J., and
                                  K. Fujiwara, "POP3 Support for UTF-8",
                                  draft-ietf-eai-rfc5721bis-00 (work in
                                  progress), September

   [Latin]                   Unicode Consortium, "C0 Controls and Basic

   [NFC]                     Davis, M. and K. Whistler, "Unicode
                             Standard Annex #15: Unicode Normalization
                             Forms", September 2010,

   [RFC2119]                 Bradner, S., "Key words for use in RFCs to
                             Indicate Requirement Levels", BCP 14,
                             RFC 2119, March 1997.

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

   [RFC5198]                 Klensin, J. and M. Padlipsky, "Unicode
                             Format for Network Interchange", RFC 5198,
                             March 2008.

   [RFC5234]                 Crocker, D. and P. Overell, "Augmented BNF
                             for Syntax Specifications: ABNF", STD 68,
                             RFC 5234, January 2008.

   [RFC5321]                      Klensin, J., "Simple Mail Transfer
                                  Protocol", RFC 5321, October 2008.

   [RFC5322]                 Resnick, P., Ed., "Internet Message
                             Format", RFC 5322, October 2008.

9.2.  Informative References

   [RFC1652]                      Klensin, J., Freed, N., Rose, M.,
                                  Stefferud, E., and D.

   [RFC5598]                 Crocker, "SMTP
                                  Service Extension for 8bit-
                                  MIMEtransport", D., "Internet Mail Architecture",
                             RFC 1652, 5598, July 1994. 2009.

   [Unicode]                 Unicode Consortium, "Unicode 6.0 Character
                             Code Charts", /charts/,

9.2.  Informative References

   [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.

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

   [RFC5280]                 Cooper, D., Santesson, S., Farrell, S.,
                             Boeyen, S., Housley, R., and W. Polk,
                             "Internet X.509 Public Key Infrastructure
                             Certificate and Certificate Revocation List
                             (CRL) Profile", RFC 5280, May 2008.

Appendix A.  Changes to support UTF-8

   This section provides a basic audit of the places in a message that
   now can permit UTF-8 rather than being restricted to ASCII, based on
   the changes to underlying ABNF.  The audit ignores rule for
   "obsolete" constructs in RFC 5322.  (This is a first cut and the list
   is likely incomplete):

   VCHAR:   quoted-pair, unstructured

      > ccontent, qcontent

      > comment, quoted-string

      > word, local-part

      > phrase

      > display-name, keywords

   ctext:   ccontent > comment

   atext:   atom, dot-atom-text

   qtext:   qcontent > quoted-string

Authors' Addresses

   Abel Yang
   4F-2, No. 9, Sec 2, Roosevelt Rd.
   Taipei,   100

   Phone: +886 2 23411313 ext 505

   Shawn Steele

   D. Crocker
   Brandenburg InternetWorking
   675 Spruce Dr.

   Phone: +1.408.246.8253

   Ned Freed
   800 Royal Oaks
   Monrovia, CA  91016-6347