Network Working Group J. Yeh, Ed.
Internet-Draft TWNIC
Expires: August 31, 2006 February 27, 2006
Internationalized Email Headers
draft-yeh-ima-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
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 31, 2006.
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 international
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 fields.
This form is permitted in transmission only if authorized by an SMTP
extension, as specified in an associated specification.
Yeh Expires August 31, 2006 [Page 1]
Internet-Draft I18N Email Headers February 2006
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. Impact on Message Header Fields . . . . . . . . . . . . . . . 6
7. Additional issue . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. POP3/IMAP . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Mailing list header fields . . . . . . . . . . . . . . . . 7
7.3. URI/IRI . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
Yeh Expires August 31, 2006 [Page 2]
Internet-Draft I18N Email Headers February 2006
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 [IMA-overview] and specified in [IMA-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 [IMA-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 the 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 messages.
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 [IMA-overview] and [IMA-SMTP-
extension], and that allows non-ASCII characters throughout email
header fields. These changes affect SMTP clients, SMTP servers, and
mail user agents (MUAs).
Yeh Expires August 31, 2006 [Page 3]
Internet-Draft I18N Email Headers February 2006
As specified in [IMA-SMTP-extension], an SMTP protocol extension
[RFC2821] is used to prevent the transmission of messages with UTF-8
header fields to systems that cannot handle such messages.
Use 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 will 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 [IMA-downgrading].
This protocol is workable even if IMA mailbox names are not
presented. For example, the protocol might still be used if just the
subject header has non-ASCII characters, but the protocol MUST be
used if other header fields (particularly trace header fields such as
"Received:") contain non-ASCII characters.
3. Terminology
In this document, header fields are "UTF-8 header" if the bodies of
headers contain UTF-8 characters.
Unless otherwise noted, all terms used here are defined in [RFC2821]
or [RFC2822] or in [IMA-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 "IMA".
Yeh Expires August 31, 2006 [Page 4]
Internet-Draft I18N Email Headers February 2006
That protocol is defined in [IMA-SMTP-extension]. If that extension
is not supported, UTF-8 header fields MUST NOT be transmitted.
Sending MUAs that follow this protocol MUST create all header fields
encoded in UTF-8. No other direct encodings are allowed. MUAs MAY
continue to use MIME to specify some text in other encodings; however
this is not recommended because it is likely that this will not
interoperate well with MUAs that follow this specification.
5. Identification of internationalized email
When a SMTP client tries to send a mail to a SMTP server that does
not support IMA, the client should know whether the message requires
the support for IMA or not. In addition to this, identifiction of
internationalized email is also required when a message is stored and
presented. Checking the presence of UTF-8 characters in the header
whenever such an identification is required may also achieve the its
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. IMA compliant) or old one (i.e. RFC 2822
compliant).
To be able to do so, sending MUA should insert a new header field to
identify the presence of i18n information (particularly UTF-8
headers) in the message. The new header specified as "i18n-email",
and elements of the header is the version number of i18n email. The
i18n header field syntax specified like:
i18n-email: 1.0
[Note in draft: There should be more useful information can be place
in the new header field. ]
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 "i18n-email" header field MUST be inserted by the originating
MUA.
o The "i18n-email" header field MUST be inserted, along with Return-
path, by the final delivery MTA if not presented.
o The "i18n-email" header field, if present, MUST be removed as part
of any downgrading process that eliminates the UTF-8 header
information.
Yeh Expires August 31, 2006 [Page 5]
Internet-Draft I18N Email Headers February 2006
o MTAs MAY check for duplicates of the "i18n-email" header field and
eliminate all but one of them. However, if a receiving MUA
encounters more than one of these headers, it SHOULD simply ignore
any excess ones.
This combination guarantees that the header will be present on
delivery even if it is deleted in transit.
6. Impact on Message Header Fields
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.
SMTP client can send header fields in UTF-8 format, if the IEmail
extensionextension advertised by SMTP server. However, the
Message-ID is the unique identifier of a single email. [Note in
draft: Extension name depends on the SMTP extension defined in [IMA-
SMTP-extension]] In order to maintain the identity, message
identifiers of the Message-ID fields MUST be created in all ASCII.
To be specific, when IEE smtp extension is advertised.
o <unstructured>, <comment> and <phrase> are allowed to use UTF-8.
o <date-time>, <msg-id> remains the same definition as in RFC2822.
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 IMA
unawareMTAs in the mail routing path. In that case, MTA may bounce
the message with reply code 558, or downgrade the non-ASCII contents
of all header bodies before continuing to send the message, as
described in [IMA-downgrading]. However, MTAs never know if there
are any data or instructions embedded in the email address. Or there
also email addresses do not contain embedded operations. The only
one way is to let the mail address owner to tell if the address is ok
for downgrade process or not. Hence, the ATOMIC and ALT-ADDRESS
options are introduced. The detail of ATOMIC and ALT-ADDRESS options
can be found in [IMA-SMTP-extension]. With these two different
cases, there are two possible representation of <mailbox>.
o ATOMIC:
ATOMIC, it means that the email address can be downgraded safely
without damage to the mail delivery. In this case, the <mailbox>
syntax remains the same to RFC2822. The only difference is that
the <local-part> and <domain> of <addr-spec> allows UTF-8
characters.
Yeh Expires August 31, 2006 [Page 6]
Internet-Draft I18N Email Headers February 2006
o ALT-ADDRESS:
If user provides an alternative address for the internationalized
email address for the mail delivery. The <mailbox> syntax will be
mailbox = new-name-addr / new-addr-spec
new-name-addr = [display-name] new-angle-addr
new-angle-addr = [CFWS] "<" new-addr-spec ">" [CFWS]
new-angle-addr =/ obs-angle-addr
new-addr-spec = [addr-spec] non-ASCII-addr-spec
new-addr-spec =/ addr-spec
In any time, SMTP server can reject with a reply code of 558 whenever
ALT-ADDRESS is not provided and downgrade is not feasible.
[Note in draft: The detail ABNF will need to be prepared in this
document when proper WG establish.]
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
IEE deployment.
7.1. POP3/IMAP
Receiving MUAs that follow this protocol MUST able to handle email
header fields encoded in UTF-8. Which means that the email fetching
protocol such as POP3 or IMAP MAY need to be updated.
7.2. Mailing list header fields
All mailing list and mail redistribution related header fields may
need further investigation.
7.3. URI/IRI
The mailto schema in URI/IRI may need further investigation.
8. Security Considerations
If a user has a non-ASCII mailbox address and a all-ASCII mailbox
address, a digital certificate that identifies that user SHOULD have
both addresses in the identity. Having multiple email addresses as
identities in a single certificate is already supported in PKIX and
OpenPGP.
Yeh Expires August 31, 2006 [Page 7]
Internet-Draft I18N Email Headers February 2006
Because UTF-8 often requires several octets to encode a single
character, internationalized local parts may cause mail addresses to
become longer. Then may possibly make it harder to keep lines in a
header under 78 octets. Lines that are longer than 78 octets (which
is a SHOULD specification, not a MUST specification, in RFC 2822)
could possibly cause mail user agents to fail in ways that affect
security.
9. IANA considerations
The ESMTP extension needed to support this specification is specified
in [IMA-SMTP-extension]. This specification does not require any
additional IANA actions in that regard.
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, 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. References
11.1. 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.
[IMA-SMTP-extension]
Yao, J., Ed. and X. LEE, "SMTP extension for
internationalized email address",
draft-yao-ima-smtpext-00.txt (work in progress),
January 2006.
Yeh Expires August 31, 2006 [Page 8]
Internet-Draft I18N Email Headers February 2006
[IMA-overview]
Klensin, J. and Y. Ko, "Overview and Framework of
Internationalized Email Address Delivery",
draft-klensin-ima-framework-00.txt (work in progress),
September 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 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.
11.2. Informative References
[]
Hoffman, P., "SMTP Service Extensions or Transmission of
Headers in UTF-8 Encoding",
draft-hoffman-utf8headers-00.txt (work in progress),
December 2003.
[IMA-downgrading]
"whatever we call the downgrading document", 2005.
[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.
Yeh Expires August 31, 2006 [Page 9]
Internet-Draft I18N Email Headers February 2006
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
Yeh Expires August 31, 2006 [Page 10]
Internet-Draft I18N Email Headers February 2006
Intellectual Property Statement
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
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
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
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
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.
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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Yeh Expires August 31, 2006 [Page 11]