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draft-ietf-eai-smtpext-08.txt --> draft-ietf-eai-smtpext-09.txt

Network Working Group J. Yao, Ed.
Internet-Draft W. Mao, Ed.
Updates: RFC4952 CNNIC
(if approved) November 17, 2007
Intended status: Experimental CNNIC
Expires: March 6, May 20, 2008 September 3, 2007

SMTP extension for internationalized email address
draft-ietf-eai-smtpext-08.txt
draft-ietf-eai-smtpext-09.txt

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This Internet-Draft will expire on March 6, May 20, 2008.

Abstract

This document specifies the use of an SMTP extension for transport and delivery
of email messages with internationalized email address delivery. addresses or header
information. Communication with systems that do not implement this
specification is specified in another document.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Role of this specification . . . . . . . . . . . . . . . . 3
1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 4
2.1. Framework for the Internationalization Extension . . . . . 4
2.2. The UTF8SMTP Extension . . . . . . . . . . . . . . . . . . 5
2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 6
2.4. The ALT-ADDRESS parameter Parameter . . . . . . . . . . . . . . . . 8
2.5. ALT-ADDRESS parameter usage Parameter Usage and response codes Response Codes . . . . . . 9
2.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 9 10
2.7. Additional ESMTP Changes and Clarifications . . . . . . . 10
2.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 10 11
2.7.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 10 11
2.7.3. Trace Information . . . . . . . . . . . . . . . . . . 10 11
2.7.4. UTF-8 Reply . . . . . . Strings in Replies . . . . . . . . . . . . . . . 11 12
3. Issues with Other Parts of the Email System . . . . . . . . . 13
3.1. LMTP . . . . . . . . . . . . . . . . . . . . . . IANA Considerations . . . . . 13
3.2. SMTP Service Extension for DSNs . . . . . . . . . . . . . 13
3.3. POP and IMAP . . . 14
4. Security Considerations . . . . . . . . . . . . . . . . . . . 14
5. Acknowledgements . 13
4. Potential problems . . . . . . . . . . . . . . . . . . . . . . 14
4.1. Impact many email related RFC . .
6. Change History . . . . . . . . . . . . 14
5. Implementation Advice . . . . . . . . . . . . 15
6.1. draft-ietf-eai-smtpext: Version 00 . . . . . . . . 14
6. IANA Considerations . . . . 15
6.2. draft-ietf-eai-smtpext: Version 01 . . . . . . . . . . . . 15
6.3. draft-ietf-eai-smtpext: Version 02 . . . . . 14
7. Security considerations . . . . . . . 15
6.4. draft-ietf-eai-smtpext: Version 03 . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . .
6.5. draft-ietf-eai-smtpext: Version 04 . . . . . . . . . . . . 15
9. Change History 16
6.6. draft-ietf-eai-smtpext: Version 05 . . . . . . . . . . . . 16
6.7. draft-ietf-eai-smtpext: Version 06 . . . . . . . . . . . . 15
9.1. 16
6.8. draft-ietf-eai-smtpext: Version 00 07 . . . . . . . . . . . . 15
9.2. 16
6.9. draft-ietf-eai-smtpext: Version 01 08 . . . . . . . . . . . . 15
9.3. 16
6.10. draft-ietf-eai-smtpext: Version 02 09 . . . . . . . . . . . . 16
9.4. draft-ietf-eai-smtpext: Version 03
7. References . . . . . . . . . . . . 16
9.5. draft-ietf-eai-smtpext: Version 04 . . . . . . . . . . . . 16
9.6. draft-ietf-eai-smtpext: Version 05 . . 17
7.1. Normative References . . . . . . . . . . 16
9.7. draft-ietf-eai-smtpext: Version 06 . . . . . . . . . 17
7.2. Informative References . . . . 16
9.8. draft-ietf-eai-smtpext: Version 07 . . . . . . . . . . . . 16
9.9. draft-ietf-eai-smtpext: Version 08 . . 18
Appendix A. Material Updating RFC 4952 . . . . . . . . . . . . 17
10. References . 18
A.1. Conventional Message and Internationalized Message . . . . 19
A.2. LMTP . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . 19
A.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 17
10.2. Informative References 19
A.4. Implementation Advice . . . . . . . . . . . . . . . . . . 18 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 20 21

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1. Introduction

Internationalized email

An internationalized email address includes two parts, the local part
and the domain part. The ways email addresses are used by protocols
are different from the ways domain names are used. The most critical
difference is that emails are delivered through a chain of peering clients
and servers while domain names are resolved by name servers
by looking
up those names in their own tables. In addition to this, the
extended email transport protocol ESMTP[RFC1869] [RFC2821] provides a negotiation
mechanism through with which clients can discover server capabilities and
make decisions for further processing; please see
more in [EAI-framework]. Email addresses can exploit processing. An extended overview of the SMTP
extension negotiation mechanism while Internationalized Domain
Name(IDN) does not have such a facility. This is also more
architecturally desirable approach. model for internationalized addresses and headers appears
in [EAI-framework], referred to as "the framework document" or just
as "Framework" elsewhere in this specification. This document
specifies an SMTP extension to permit internationalized email
addresses in envelopes, and UTF-8 UNICODE characters (encoded in UTF-8) in
headers. The protocol described here is an MTA solution
which is feasible, architecturally elegant, and not difficult to
deploy.

1.1. Role of this specification

The framework document [EAI-framework] specifies the requirements for, and describes
components of, full internationalization of electronic mail.
To understand and implement this specification, A
thorough understanding of the
context presented information in [EAI-framework] that document and in the
base Internet email specifications [RFC2821] [RFC2822] is necessary. necessary
to understand and implement this specification.

This document specifies an element of that the email internationalization
work, specifically the definition of an SMTP extension [RFC1869] [RFC2821] for the
internationalized email address transport delivery.

1.2. Proposal Context

This specification describes a change an optional extension to the email
transport mechanism that permits non-ASCII [ASCII] characters in both
the envelope and header fields of messages while the messages. The EAI-utf8header
specification in [EAI-utf8header]
specifies provides the details of how and where
non-ASCII characters are permitted in the header fields of messages.
The context for the change is described in [EAI-framework]. the framework document.

1.3. Terminology

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

The terms "conventional message" and "internationalized message" are
defined in an appendix to this specification. The terms "UTF-8
string" or "UTF-8 character" are used informally to refer to Unicode

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characters encoded in UTF-8 [RFC3629]. All other specialized terms
used in this specification are defined in the
EAI framework [EAI-framework] document or
in the base Internet email specifications [RFC2821] and [RFC2822]. The In
particular, the terms "ASCII address", "internationalized email
address", "non-ASCII

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Internet-Draft EAI September 2007 address", "i18mail address", "UTF8SMTP",
"message" and "mailing list" are used with in this document according to
the definitions from in the [EAI-framework] document. framework one.

This document specification defines only those ABNF [RFC4234] syntax rules
that are different from those of the base email specifications
[RFC2821][RFC2822] and, where the earlier rules are upgraded or
extended, gives them new names. When the new rule is a small upgrade
modification to the older one, it is typically given a name starting
with "u". Rules that are undefined here may be found in the base
email
documents specifications under the same names.

[[anchor4: NOTE TO RFC EDITOR'S NOTE: The EDITOR: Please remove the following text should be deleted
before publication.]]
This document specification is being discussed on the EAI 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.

2. Mail Transport-level Protocol

2.1. Framework for the Internationalization Extension

The following service extension is defined:

1. The name of the SMTP service extension is "Email Address
Internationalization";
Internationalization".
2. The EHLO keyword value associated with this extension is
"UTF8SMTP";
"UTF8SMTP".
3. No parameter values are defined for this EHLO keyword value. In
order to permit future (although unanticipated) extensions, the
EHLO response MUST NOT contain any parameters for that keyword.
Clients MUST ignore any parameters, that is, clients MUST behave
as if the parameters do not appear. If a server includes
UTF8SMTP in its EHLO response, it MUST be fully compliant with
this version of this specification.
4. One optional parameter, ALT-ADDRESS, is added to the SMTP MAIL and
RCPT commands. commands of SMTP. ALT-ADDRESS specifies an all-ASCII
address which can be used as a substitute for the i18mail addresses that
we call the corresponding
primary address; you can learn more (i18mail) address when downgrading. More discussion of
the use of this parameter appears in [EAI-framework] or and
[EAI-downgrading].

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5. One optional parameter "UTF8REPLY" is added to the VRFY and EXPN
commands. The parameter UTF8REPLY has no value. The parameter
indicates that the SMTP client can accept Unicode characters in
UTF-8 on encoding in replies of from the VRFY and EXPN commands.
6. No additional SMTP verbs are defined by this extension.
7. Servers offering this extension MUST provide support for, and
announce, the 8BITMIME extension [RFC1652].

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8. The reverse-path and forward-path of the SMTP MAIL and RCPT
commands are extended to allow UTF-8 Unicode characters encoded in
UTF-8 in the specified mailbox
address. names (addresses).
9. The mail datum message body is extended as specified in compliance with [EAI-utf8header]
[EAI-utf8header].
10. The maximum length of a MAIL and RCPT command lines is increased
by 460 characters by the possible addition of the ALT-ADDRESS
keyword and value.
11. The UTF8SMTP extension is valid on the submission port
[RFC4409].

2.2. The UTF8SMTP Extension

An SMTP Server that announces this extension MUST be prepared to
accept a UTF-8 string [RFC3629] in any position in which RFC 2821
specifies that a "mailbox" MAY mailbox can appear. That string MUST be parsed only
as specified in RFC 2821, i.e., by separating the mailbox into source
route, local part and domain part, using only the characters colon
(U+003A), comma (U+002C), and at-sign (U+0040) as specified there.
Once isolated by this parsing process, the local part MUST be treated
as opaque unless the SMTP Server is the final delivery MTA. Any
domain names that are to be looked up in the DNS MUST first be
processed into the form specified in IDNA [RFC3490] by means of the
ToASCII() operation unless they are already in that form. Any domain
names that are to be compared to local strings SHOULD be checked for
validity and then MUST be compared as specified in section 3.4 of
IDNA.

The UTF8SMTP extension is valid on the submission port [RFC4409].

An SMTP Client that receives the UTF8SMTP extension keyword in
response to the "EHLO" command MAY transmit a mailbox name names within SMTP
commands as an internationalized string strings in UTF-8 form and form. It MAY send an a
UTF-8 header
[EAI-utf8header]. [EAI-utf8header] (which may also include mailbox names
in UTF-8). It MAY transmit the domain part parts of that string mailbox names within
SMTP commands or the message header in either the form of ACE labels
as specified in IDNA [RFC3490] or as UTF-8 form.
In the strings. All labels in
domain part parts of the mailbox string, if any of the labels names which are
intended to IDNs (either UTF-8 or ACE
strings) MUST be interpreted as non-ASCII (i.e., are IDNs), then valid. If the original client submits a message to
a Message Submission Server ("MSA") [RFC4409] MUST take [RFC4409], it is the
responsibility
for ensuring that of the MSA that all domain labels are valid (whether they appear in native
character or ACE form). valid; otherwise
it is the original client's responsibility. The presence of the
UTF8SMTP extension does not change the requirement of RFC 2821 that

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servers relaying mail MUST not attempt to parse, evaluate, or
transform the local part in any way.

If the UTF8SMTP SMTP extension is not offered by the Server, the SMTP
client MUST NOT transmit an internationalized address and MUST NOT
transmit a mail message which contains containing internationalized mail headers as
described in [EAI-utf8header] at any level within its MIME structure.
Instead, if an SMTP client (SMTP sender) attempts to transfer a UTF8SMTP
internationalized message and encounters a server that does not
support the extension, it MUST make one of the following four
choices:

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1. If and only if the SMTP client (sender) is a Message Submission
Server[RFC4409],
Server ("MSA") [RFC4409], it MAY, consistent with the general
provisions for changes by such servers, rewrite the envelope,
headers, or message material to make them entirely ASCII and
consistent with the provisions of RFC 2821 [RFC2821] and RFC 2822
[RFC2822].
2. Reject Either reject the message during the SMTP transaction or accept
the message and then generate and transmit a notification of non-deliverability, non-
deliverability. Such notification MUST be done as specified in
RFC 2821
[RFC2821] and [RFC2821], RFC 3464 [RFC3464]. If the message content can be
returned without alteration, content should be returned as
specified in 2821 but, if a server is encountered along the
return path that cannot accept UTF8SMTP traffic, [RFC3464], and the content
should simply be abridged or dropped. EAI DSN
specification [EAI-dsn].
3. Find an alternate route to the destination that permits UTF8SMTP.
That route may be discovered by trying alternate MX hosts (using
preference rules as specified in RFC 2821) or using other means
available to the SMTP-sender.
4. If and only if ASCII addresses are available for all addresses
that appear in the return path and the specific forward paths
being attempted, downgrade the message to an all-ASCII form as
specified in [EAI-downgrading]. An ASCII address is considered
to be "available" for a particular address if the original
address in the envelope is in ASCII or if an ALT-Address ALT-ADDRESS
parameter is specified for a UTF8SMTP address.

2.3. Extended Mailbox Address Syntax

RFC 2821, section 4.1.2, defines the syntax of a mailbox entirely in
terms of ASCII characters, using the production for "Mailbox" a mailbox and
those on which it depends.

The key changes made by this specification are, informally, to

o Change the definition of "sub-domain" to permit either the
definition above or a UTF-8 string representing a DNS label that
is conformant with IDNA [RFC3490].
o Change the definition of "Atom" to permit either the definition
above or

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o Change the definition of "Atom" to permit either the definition
above or a UTF-8 string. That string MUST NOT contain any of the
ASCII characters (either graphics or controls) that are not
permitted in "atext"; it is otherwise unrestricted.

According to the description above, define the syntax of an
internationalized email mailbox with name (address) is defined in ABNF
[RFC4234] as

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uMailbox = uLocal-part "@" uDomain
; Replace Mailbox in RFC 2821, section 4.1.2

uLocal-part = uDot-string / uQuoted-string
; MAY be case-sensitive
; Replace Local-part in RFC 2821, section 4.1.2

uDot-string = uAtom *("." uAtom)
; Replace Dot-string in RFC 2821, section 4.1.2

uAtom = 1*ucharacter
; Replace Atom in RFC 2821, section 4.1.2

ucharacter = atext / UTF8-xtra-char
; Replace character in RFC 2821, section 4.1.2
; atext is defined in RFC 2822

uQuoted-string = DQUOTE *uqcontent DQUOTE
; Replace Quoted-string in RFC 2821, section 4.1.2
; DQUOTE is Double Quote defined in RFC 4234

uqcontent = qcontent / UTF8-xtra-char
; qcontent is defined in RFC 2822, section 3.2.5

uDomain = (sub-udomain 1*("." sub-udomain)) / address-literal
; Replace Domain in RFC 2821, section 4.1.2
; address-literal is defined in RFC2821 section 4.1.2

sub-udomain = uLet-dig [uLdh-str]
; Replace sub-domain in RFC 2821, section 4.1.2

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uLet-dig = Let-dig / UTF8-xtra-char
; Let-dig is defined in RFC 2821, section 4.1.3

uLdh-str = *( ALPHA / DIGIT / "-" / UTF8-xtra-char) uLet-dig
; Replace Ldh-str in RFC 2821, section 4.1.3

UTF8-xtra-char = UTF8-2 / UTF8-3 / UTF8-4
; UTF8-2, UTF8-3 and UTF8-4 are two, three, or four
; octet UTF-8 characters, as defined in RFC 3629

The value of "udomain" SHOULD be verified with by applying the tests
specified as part of IDNA [RFC3490]; [RFC3490]. If
failed, that verification fails, the
email address with that udomain can not MUST NOT be regarded as
the a valid email
address.

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2.4. The ALT-ADDRESS parameter Parameter

If the UTF8SMTP extension is offered, the syntax of the SMTP MAIL and
RCPT commands is extended to support the optional esmtp-keyword "ALT-
ADDRESS", which
ADDRESS". That keyword specifies an alternate all-ASCII address
which may be used when downgrading. If the ALT-ADDRESS esmtp-keyword
is used, it MUST have an associated esmtp-value (ALT-ADDRESS-esmtp-value (ALT-ADDRESS-esmtp-
value, which is defined below).

Based on the definition of mail-parameters in [RFC2821], the ALT-
ADDRESS parameter usage in the commands of "MAIL" and "RCPT" is
defined below. as follows. The following definitions are given in the same
format as used in RFC 2821.

"MAIL FROM:" ("<>" / uReverse-path) [ SP Mail-parameters ] CRLF
; Update mail the MAIL command in RFC 2821, section 4.1.1.2.
; A new parameter defined by the ABNF non-terminal
; <ALT-ADDRESS-parameter> is added. It complies
; with the syntax specified by <esmtp-param>. for <esmtp-param> in RFC 2821.

"RCPT TO:" ("<Postmaster@" domain uDomain ">" / "<Postmaster>" /
uForward-Path) [ SP Rcpt-parameters ] CRLF
; Update rcpt RCPT command in RFC 2821, section 4.1.1.3.
; A new parameter defined by the ABNF non-terminal
; <ALT-ADDRESS-parameter> is added. It complies
; with the syntax specified by for <esmtp-param>.
; uDomain is defined in section 2.3 of this document

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uReverse-path = uPath
; Replace Reverse-path in RFC 2821, section 4.1.2

uForward-path = uPath
; Replace Forward-path in RFC 2821, section 4.1.2

uPath = "<" [ A-d-l ":" ] uMailbox ">"
; Replace Path in RFC 2821, section 4.1.2
; A-d-l is defined in RFC 2821, section 4.1.2
; uMailbox is defined in section 2.3 of this document

ALT-ADDRESS-parameter="ALT-ADDRESS=" ALT-ADDRESS-esmtp-value

ALT-ADDRESS-esmtp-value=xtext ALT-ADDRESS-value

ALT-ADDRESS-value=xtext
; Mailbox The value is a mailbox name encoded as xtext.
; xtext is defined in RFC 3461 [RFC3461], 3461, section 4.2

The ALT-ADDRESS-parameter MUST NOT appear more than once in any MAIL
or RCPT command. ALT-ADDRESS-esmtp-value MUST be an all-ASCII email

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address before xtext encoding.

2.5. ALT-ADDRESS parameter usage Parameter Usage and response codes

[EAI-utf8header] specifies "UTF8SMTP Response Codes

An "internationalized message" which requires UTF8SMTP
support. Such a message as defined in the appendix of this
specification MUST NOT be sent to an SMTP server which that does not
support UTF8SMTP. Such a message MAY be rejected due to
lack of the ALT-ADDRESS by a server if it
lacks one or more ALT-ADDRESSes as discussed in section Section 2.2 of this document.
specification.

The three-digit reply codes used in this section are consistent with
their meanings as defined in RFC 2821.

When messages are rejected because they require UTF8SMTP, the RCPT command requires an ALT-
ADDRESS, the response code "550" 553 is used, defined in [RFC2821], used with the meaning "mailbox
unavailable". If enhanced mail system status codes [RFC3463] name
not allowed". When messages are
used, the response code rejected for other reasons, such as
the MAIL command requiring an ALT-ADDRESS, the response code 550 is
used with the meaning "mailbox unavailable". If enhanced mail system
status codes [RFC3463] are used, the response code should be "5.6.x"
[SMTP-codes], meaning that "The alt-address ALT-ADDRESS is required but not
specified".

If the response code is issued after the final "." of the DATA
command, the response code "554" is used, defined in [RFC2821], used with the meaning
"Transaction failed". If enhanced mail system status codes [RFC3463]

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are used, the response code should be "5.6.z" [SMTP-codes], meaning
that "UTF8SMTP downgrade failed".

[[anchor8: REMOVE THIS: IANA

[[anchor7: RFC Editor: please assign insert the proper error codes for
"5.6.x" and "5.6.z".]] "5.6.z" after IANA has made the relevant assignments.]]

2.6. Body Parts and SMTP Extensions

Since there is no ESMTP parameter which tells whether the message is
UTF8SMTP
an internationalized message, an SMTP server needs that requires accurate
knowledge of whether a message is internationalized is required to
parse all message header fields and MIME header fields in the message body to discover which
messages are UTF8SMTP.
body. While this specification requires that servers support the
8BITMIME extension [RFC1652] to ensure that servers have adequate
handling capability for 8-bit data and to avoid a number of complex
encoding problems, the use of internationalized addresses obviously
does not require non-ASCII body parts in the MIME message. The
UTF8SMTP extension MAY be used with the BODY=8BITMIME parameter if
that is appropriate given the body content or, if the server
advertises it BINARYMIME [RFC3030] and it the BODY=BINARYMIME is
appropriate, with the BODY=BINARYMIME
parameter specified in [RFC3030]. parameter.

Assuming that the server advertises UTF8SMTP and 8BITMIME, and
receives at least one non-ASCII address, with or without ALT-ADDRESS,
the precise interpretation of "No 'Body' parameter", "BODY=
8BITMIME", and "BODY= BINARYMIME" in the MAIL command is:
1. For No If there is no "Body" parameter, headers are in UTF-8, the header contains UTF-8
characters but all the body parts are in
ASCII. ASCII (possibly as the
result of a Content-transfer-encoding).
2. For If a BODY=8BITMIME parameter, headers are in UTF-8, parameter is present, the header contains
UTF-8 characters and some or all of the body parts contain 8-bit
line-oriented data.

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3. For If a BODY=BINARYMIME parameter, headers are in UTF-8, parameter is present, the header contains
UTF-8 characters and some or all body parts contain binary data
without restriction as to line lengths or delimiters.

2.7. Additional ESMTP Changes and Clarifications

The information carried in the mail transport process involves
addresses ("mailboxes") and domain names in contexts in addition to
the MAIL and RCPT commands and extended alternatives to them. In
general, the rule is that, when RFC 2821 specifies a mailbox, this document
specification expects UTF-8 to be used for the entire string; when
RFC 2821 specifies a domain name, the name SHOULD be in the form of
ACE labels if its raw form is non-
ASCII. non-ASCII.

The following subsections list and discuss all of the relevant cases.

Support and use of this extension requires support for 8BITMIME. It
means that 8BITMIME MUST be advertised by the UTF8SMTP capable

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server. Extension November 2007

2.7.1. The Initial SMTP Exchange

When an SMTP or ESMTP connection is opened, the server normally sends
a "greeting" response consisting of the '220' reply code and some
information. The client then sends the EHLO command. Since the
client cannot know whether the server supports UTF8SMTP until after
it receives the response from EHLO, any domain names that appear in
this dialogue, or in responses to EHLO, MUST be in the hostname form,
i.e., internationalized ones MUST be in the form of ACE labels.

2.7.2. Mail eXchangers

Commonly, organizations

Organizations often authorize multiple servers to accept mail
addressed to them. For example, the organization may itself operate
more than one server, and may also or instead have an agreement with
other organizations to accept mail as a backup. Authorized servers
are generally listed in MX records [RFC2821]. as described in RFC2821. When
more than one server accepts mail for the domain-part of a Mailbox, mailbox,
it is strongly advised that either all or none of them support the
UTF8SMTP extension. Otherwise, surprising downgrades can happen
during temporary failures, which is not a good thing.

2.7.3. Trace Information

When an SMTP server receives a message for delivery or further
processing, it MUST insert trace ("time stamp" or "Received")
information at the beginning of the message content. Time stamp "Time stamp" or
"Received" appears in the form of "Received: lines". The most
important use of

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the delivery SMTP server makes the "final delivery" of a message, it
inserts a return-
path return-path line at the beginning of the mail data. The
primary purpose of the Return-path is to designate the address to
which messages indicating non-delivery or other mail system failures
are to be sent. For the trace information, we update this memo updates the
time stamp line and the return path line [RFC2821] formally defined
as follows:

uReturn-path-line = "Return-Path:" FWS uReverse-path <CRLF>
; Replaces Return-path-line in the section 4.4 of [RFC2821] RFC2821
; uReverse-path is defined in Section 2.3 of this document

uTime-stamp-line = "Received:" FWS uStamp <CRLF>
; Replaces Time-stamp-line in the section 4.4 of [RFC2821] RFC2821

uStamp = From-domain By-domain uOpt-info ";" FWS date-time
; Replaces Stamp in the section 4.4 of [RFC2821] RFC2821

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uOpt-info = [Via] [With] [ID] [uFor]
; Replaces Opt-info in the section 4.4 of [RFC2821] RFC2821
; [With]'s The protocol value for With will allow a UTF8SMTP value

uFor = "FOR" 1*( ( FWS (uPath / uMailbox) ) CFWS
; Replaces For in the section 4.4 of [RFC2821] RFC2821
; uPath is and uMailbox are defined in section Sections 2.4 of this document and
; uMailbox is defined in section 2.3 2.3, respectively, of this document

[[anchor12:

[[anchor11: Note: Whether the The FOR parameter is permitted has been changed to accept
more than match the
definition in RFC2821bis, permitting only one address is now under discussion as part of in the
rfc2821bis effort. For
clause. The multiple-address construction was introduced
with RFC 2821; it is not clear that it has been widely implemented or group working on that it is wise. Whatever decision is document reached about RFC2821bis will
be reflected in mailing list
consensus that the syntax of in RFC 2821 that permitted more than one
address was simply a future version of this document.]] mistake.]]
Except in the 'uFor' and 'uReverse-path' line where non-ASCII domain
name
names may be used, internationalized domain names in Received fields
MUST be transmitted in the form of ACE labels. The protocol value of
the WITH clause is UTF8SMTP when this extension is used. More
information is in the "IANA Considerations" section of this document.
specification.

2.7.4. UTF-8 Reply Strings in Replies

2.7.4.1. MAIL and RCPT Commands

If the client issues the RCPT command which contains containing non-ASCII
characters, the SMTP server is permitted to use UTF-8 characters in
the email address within associated with 251 and 551 response codes.

If an SMTP client follows this specification and sends any RCPT

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commands containing non-ASCII addresses, it MUST be able to accept
and process 251 or 551 replies containing UTF-8 email addresses. If
a given RCPT command does not include a non-ASCII envelope addresses, address,
the server MUST not return a 251 or 551 response containing a non-
ASCII mailbox. Instead, it MUST transform such responses into 250 or
550 responses that do not contain addresses.

2.7.4.2. VRFY and EXPN Commands and the UTF8REPLY Parameter

If the VRFY and EXPN commands have are transmitted the optional parameter
"UTF8REPLY", it indicates the client can accept UTF-8 on strings in
replies of
the VRFY and EXPN from those commands. Specially this This allows the server to use UTF-8 on
mailboxes
strings in mailbox names and full names which occur on replies. The in replies
without concern that the client might be confused by them. An SMTP
client
following that conforms to this specification MUST accept UTF-8 on and correctly
process replies of from the VRFY and EXPN commands. commands that contain UTF-8
strings. However the SMTP server MUST not NOT use UTF-8 on
replies, strings in

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replies if the SMTP client does not ask UTF-8 replies. Some specifically allow such replies
include the mailbox, but usually most of
by transmitting this parameter. Most replies do not require that
the a
mailbox is name be included in it the returned text and therefore UTF-8 is
not needed. The
UTF8REPLY parameter on needed in them. Some replies, notably those resulting from
successful execution of the VRFY and EXPN commands tells commands, do include the SMTP
server that
mailbox, making the client is prepared for UTF-8 on SMTP replies. provisions of this section important.

VERIFY (VRFY) and EXPAND (EXPN)command syntaxes are changed to:

"VRFY" SP (uLocal-part / uMailbox) [SP "UTF8REPLY"] CRLF;
;uLocal-part is CRLF
; uLocal-part and uMailbox are defined in section 2.3 of this document
;uMailbox is defined in section
: Section 2.3 of this document

"EXPN" SP (uLocal-part ( uLocal-part / uMailbox) [SP "UTF8REPLY"] CRLF;
;uLocal-part is uMailbox ) [ SP "UTF8REPLY" ] CRLF
; uLocal-part and uMailbox are defined in section
; Section 2.3 of this document
;uMailbox

There is defined in section 2.3 of this document

This parameter no value associated with the "UTF8REPLY" does not have value. parameter. If SMTP
reply requires UTF-8, but SMTP client does not use "UTF8REPLY"
parameter in the VERIFY (VRFY) and EXPAND (EXPN) commands, the
response code 252 is used, defined in [RFC2821], meaning "Cannot VRFY
user, but will accept the message and attempt the delivery". Also
response code 550 may be used, meaning "Requested action not taken:
mailbox unavailable". If enhanced mail system status code [RFC3463]
is used, response codes given on below is used. "UTF8REPLY" on the
VERIFY (VRFY) or EXPAND (EXPN) commands enables UTF-8 for that
command only.

If a normal success response (i.e., 250) response is returned, the response
MAY include the full name of the user and MUST include the mailbox of
the user. It MUST be in either of the following forms:

User Name <uMailbox>
; uMailbox is defined in section 2.3 of this document
; User Name allows the can contain non-ASCII character. characters.

uMailbox

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; uMailbox is defined in section 2.3 of this document

If the SMTP reply requires UTF-8, UTF-8 strings, but UTF-8 is not allowed on in
the reply, and enhanced mail system status code codes [RFC3463] is are used,
the response code should be "5.6.y" or "2.6.y" [SMTP-codes], meaning
that "The
UTF-8 "A reply required, containing a UTF-8 string is required to show the
mailbox name, but that form of response is not allowed.". [[anchor13: REMOVE THIS:
IANA please assign permitted by the proper error codes for "5.6.y" and "2.6.y".]]
client.".

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If the SMTP Client lack of does not support the UTF8SMTP support service extension,
but receives a the UTF-8
message on string in a reply, it may not be able to
properly report the reply to the user or even crash. UTF-8
Internationalized messages on reply in replies are only allowed in the
commands under the situations described above. Under any other
circumstances, UTF-8 messages on the reply text MUST NOT be
used. appear in the reply.

Although UTF-8 is needed to represent email addresses in responses
under the rules specified in this section, this extension does not
permit the use of UTF-8 for any other purposes. SMTP servers MUST
NOT include non-ASCII characters in replies except in the limited
cases specifically permitted in this section.

3. Issues with Other Parts of IANA Considerations

IANA is requested to add "UTF8SMTP" to the Email System

3.1. LMTP

LMTP [RFC2033] may be used as SMTP extensions registry
with the final delivery agent. In such
cases, LMTP may be arranged entry pointing to deliver the mail this specification for its definition.

IANA is requested to assign the mail store. proper error codes for "5.6.x",
"5.6.z", "5.6.y" and "2.6.y", following the guidance in Section 2.5,
and based on [SMTP-codes] and enter them in the appropriate registry.

The mail store may not have UTF8SMTP capability. LMTP need "Mail Transmission Types" registry is requested to be updated to deal with these situations.

3.2. SMTP Service Extension for DSNs

The existing draft standard Delivery status notifications
(DSNs)[RFC3461] is presently limited to US-ASCII text in the machine
readable portions of
include the protocol. "International Delivery and
Disposition Notifications" [EAI-dsn] adds a following new address type for
international email addresses so an original recipient address entries:

4. Security Considerations

See the
DSN extension, that server MUST implement EAI-dsn [EAI-dsn] including
support for extended security considerations discussion in the ORCPT parameter.

3.3. POP and IMAP

The [EAI-framework] has introduced two documents [EAI-pop] and
[EAI-imap] to how to use internationalized user names based on UTF-8
characters for framework
document [EAI-framework].

5. Acknowledgements

Much of the retrieval text in the initial version of messages from a mail server. this specification was

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4. Potential problems

4.1. Impact many email related RFC

Internationalized email has implications for all processes and
protocols which examine, handle, generate,

derived or otherwise deal copied from [Klensin-emailaddr] with
mail. In particular, address parsing or validity checks, message
parsing or handling, etc.

5. Implementation Advice

In the absence permission of this extension, SMTP clients the
author. Significant comments and servers are
constrained to using only those addresses permitted by RFC 2821. The
local parts of those addresses MAY be made up suggestions were received from
Xiaodong LEE, Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other
members of any ASCII
characters, although some the JET team and were incorporated into the specification.
Additional important comments and suggestions, and often specific
text, were contributed by many members of them MUST be quoted as specified there.
It is notable in an internationalization context that there is a long
history on some systems of using overstruck ASCII characters (a
character, a backspace, and another character) within a quoted string
to approximate non-ASCII characters. This form of
internationalization SHOULD be phased out as this extension becomes
widely deployed but backward-compatibility considerations require
that it continue to be supported.

6. IANA Considerations

IANA is requested to add "UTF8SMTP" to the SMTP extensions registry
with the entry pointing to this specification for its definition.

IANA is requested to assign the proper error codes "5.6.x", "5.6.z",
"5.6.y" WG and "2.6.y" for this specification based on [SMTP-codes].

The "Mail Transmission Types" registry is requested to be updated to design team.
Those contributions include the following new entries:

WITH protocol types Description Reference
------------------- ---------------------------- ---------
UTF8SMTP UTF8SMTP with Service Extensions [RFCxxxx]
UTF8SMTPA UTF8SMTP with SMTP AUTH [RFC2554bis]
[RFCxxxx]
UTF8SMTPS UTF8SMTP with STARTTLS [RFC3207]
[RFCxxxx]
UTF8SMTPSA UTF8SMTP with both STARTTLS and [RFC3207]
SMTP AUTH [RFC2554bis]
[RFCxxxx]

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[[anchor22: REMOVE THIS: where RFCxxxx represents the future RFC N0.
of this document. When this document is published as RFC and
assigned with a RFC No., "xxxx" should be replaced with 4-digits No..
"RFC2554bis" should be replaced with the new RFC No. when the
"RFC2554bis" document is assigned with the new RFC No.]]

7. Security considerations

See the extended security considerations discussion in
[EAI-framework]

8. Acknowledgements

Much of the text in the initial version of this document was derived
or copied from [Klensin-emailaddr] with the permission of the author.
Significant comments and suggestions were received material from Xiaodong LEE,
Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other members of the JET
team and were incorporated into the document. Special thanks to
those contributors for this version of the document, those include
(but not limited to) John C Klensin, Charles
Lindsey, Dave Crocker, Harald Tveit Alvestrand, Marcos Sanz, Chris
Newman, Martin Duerst, Edmon Chung, Tony Finch, Kari Hurtta, Randall
Gellens, Frank Ellermann, Alexey Melnikov. Melnikov, Pete Resnick, S.M., and
Soobok Lee. Of course, none of the individuals are necessarily
responsible for the combination of ideas represented here.

6. Change History

[[anchor25: REMOVE THIS: This section is used for tracking the update
of this document. It may be useful to retain parts of it to
facilitate establishing dates and documents for the history of

[[anchor17: RFC Editor: Please remove this
work.]]

9.1. section.]]

6.1. draft-ietf-eai-smtpext: Version 00

This version supercedes draft-yao-ima-smtpext-03.txt. It refines the
ABNF definition of the internationalized email address. It
represents as the EAI working group document.

9.2.

6.2. draft-ietf-eai-smtpext: Version 01

o Upgraded to reflect discussions during IETF 66.
o Remove the atomic parameter.

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o Add the new section of "the Suggestion of the value of the ALT-
ADDRESS parameter".

9.3.

6.3. draft-ietf-eai-smtpext: Version 02

o Upgraded to reflect the recent discussion of the ima@ietf.org
mailing list.
o Add the section of "Body Parts and SMTP Extensions".
o Add the new section of "Change History".
o Add the subsection about SMTP extensions for DSN.

9.4.

6.4. draft-ietf-eai-smtpext: Version 03

o Update the syntax related to mailbox.
o Update the trace field section.
o Add the new section about message retry.
o Update the subsection about SMTP extensions for DSN.

9.5.

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6.5. draft-ietf-eai-smtpext: Version 04

o Refine some syntax.
o Delete "Message Header Label" section.
o Change "bounce" to "reject".

9.6.

6.6. draft-ietf-eai-smtpext: Version 05

o Refine the abstract.
o Delete "The Suggestion of the Value of the ALT-ADDRESS parameter"
section.
o Move original section 2.7.4 and 2.7.5 to section 3 with the name
"Issues with other parts of the email system".
o Add the new section "LMTP".
o Refine some text according to suggestions from the EAI mailing
list discussion
o Remove the section "Mailing List Question"

9.7.

6.7. draft-ietf-eai-smtpext: Version 06

o Delete the section about message retry.
o Add the new subsection about Mail eXchangers
o Add the new section about "UTF-8 Reply"
o Refine some response code for the section "Using the ALT-ADDRESS
parameter"

9.8.

6.8. draft-ietf-eai-smtpext: Version 07

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o Rename the section 2.5
o Refine sthe section 2.7

9.9.

6.9. draft-ietf-eai-smtpext: Version 08

o Refine some texts and update some references

10.

6.10. draft-ietf-eai-smtpext: Version 09

o Add the appendix
o Move section 3.1, 3.2 and section 5 to Appendix
o Remove section 3.3 and section 4
o Add the new term definitions of conventional message and
international message in the appendix
o Refine some texts according to suggestions from the EAI mailing
list discussion during WG Last call
o Use the same reference for ASCII as RFC 2821.
o General editorial revision and cleanup, including extensive
modifications to the XML to produce a version that has better odds
of getting through the various checkers and validators.

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7. References

10.1.

7.1. Normative References

[ASCII] Cerf, V., "ASCII format American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for network interchange", RFC 20,
October 1969.
Information Interchange", ANSI X3.4-1968, 1968.

[EAI-dsn] Newman, C. and A. Melnikov, "SMTP extensions for DSNs",
draft-ietf-eai-dsn-03.txt (work in progress),
September 2007.

[EAI-framework]
Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 4952, July 2007.

[EAI-utf8header]
Abel, Y., "Transmission of Email Headers in UTF-8
Encoding", draft-ietf-eai-utf8headers-07.txt (work in
progress), September 2007.

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

[RFC1869] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extensions", STD 10, RFC 1869,
November 1995.

[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.

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

[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, January 2003.

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

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

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

[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.

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

7.2. Informative References

[EAI-downgrading]
YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading
mechanism for Internationalized eMail Address",
draft-ietf-eai-downgrade-04 (work in progress), 7 2007.

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

[RFC2033] Myers, J., "Local Mail Transfer Protocol", RFC 2033,
October 1996.

[RFC3030] Vaudreuil, G., "SMTP Service Extensions for Transmission
of Large and Binary MIME Messages", RFC 3030,
December 2000.

[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.

[RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension
for Authentication", RFC 4954, July 2007.

[SMTP-codes]
KLensin, J., "An IANA Registry for Extended SMTP Status
Codes", draft-klensin-smtp-code-registry-00 (work in
progress), April 2007.

Appendix A. Material Updating RFC 4952

RFC 4952, the Overview and Framework document covering this set of
extensions for internationalized email [EAI-framework], was completed
before this specification, which specifies a particular part of the
protocol set. This appendix, which is normative, contains material
that would have been incorporated into RFC 4952 had it been delayed
until the work described in the rest of this specification was

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[RFC4234] Crocker, D. 2007

completed and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", that should be included in any update to RFC 4234, October 2005.

10.2. Informative References

[EAI-downgrading]
YONEYA, Y., Ed. 4952.

A.1. Conventional Message and K. Fujiwara, Ed., "Downgrading
mechanism for Internationalized eMail Address",
draft-ietf-eai-downgrade-04 (work Message

o A conventional message is one that does not use any extension
defined in progress), 7 2007.

[EAI-dsn] Newman, C. this document or in the UTF8header specification
[EAI-utf8header], and A. Melnikov, "SMTP strictly conformant to RFC 2822 [RFC2822].
o An internationalized message is a message utilizing one or more of
the extensions for DSNs",
draft-ietf-eai-dsn-03.txt (work defined in progress), 9 2007.

[EAI-imap]
Resnick, P. and C. Newman, "Considerations for IMAP this specification or in
Conjunction the UTF8header
specification [EAI-utf8header], so that it is no longer conformant
to the RFC 2822 specification of a message.

A.2. LMTP

LMTP [RFC2033] may be used as the final delivery agent. In such
cases, LMTP may be arranged to deliver the mail to the mail store.
The mail store may not have UTF8SMTP capability. LMTP need to be
updated to deal with Email Address Internationalization",
draft-ietf-eai-imap-utf8-01 (work these situations.

A.3. SMTP Service Extension for DSNs

The existing draft standard Delivery status notifications
(DSNs)[RFC3461] is limited to ASCII text in progress),
March 2007.

[EAI-mailing list]
Gellens, R. the machine readable
portions of the protocol. "International Delivery and E. Chung, "Mailing Lists Disposition
Notifications" [EAI-dsn] adds a new address type for international
email addresses so an original recipient address with non-ASCII
characters can be correctly preserved even after downgrading. If an
SMTP server advertises both the UTF8SMTP and
Internationalized Email Addresses",
draft-ietf-eai-mailinglist-01.txt (work in progress),
January 2007.

[EAI-pop] Newman, C., "POP3 Support the DSN extension, that
server MUST implement EAI-dsn [EAI-dsn] including support for UTF-8",
draft-ietf-eai-pop-01.txt (work in progress),
January 2007.

[Klensin-emailaddr]
Klensin, J., "Internationalization the
ORCPT parameter.

A.4. Implementation Advice

In the absence of Email Addresses",
draft-klensin-emailaddr-i18n-03 (work in progress),
July 2005.

[RFC2033] Myers, J., "Local Mail Transfer Protocol", this extension, SMTP clients and servers are
constrained to using only those addresses permitted by RFC 2033,
October 1996. 2821. The
local parts of those addresses MAY be made up of any ASCII
characters, although some of them MUST be quoted as specified there.
It is notable in an internationalization context that there is a long
history on some systems of using overstruck ASCII characters (a
character, a backspace, and another character) within a quoted string
to approximate non-ASCII characters. This form of
internationalization SHOULD be phased out as this extension becomes
widely deployed but backward-compatibility considerations require
that it continue to be supported.

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[RFC2554bis]
Siemborski, R. and A. Melnikov, "SMTP Service Extension
for Authentication", draft-siemborski-rfc2554bis-09 (work
in progress), April 2007.

[RFC3030] Vaudreuil, G., "SMTP Service Extensions for Transmission
of Large and Binary MIME Messages", RFC 3030,
December 2000.

[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.

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

[SMTP-codes]
KLensin, J., "An IANA Registry for Extended SMTP Status
Codes", draft-klensin-smtp-code-registry-00 (work in
progress), April 2007. Extension November 2007

Authors' Addresses

Jiankang YAO (editor)
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing

Phone: +86 10 58813007
Email: yaojk@cnnic.cn

Wei MAO (editor)
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing

Phone: +86 10 58813055
Email: maowei_ietf@cnnic.cn

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Full Copyright Statement

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, THE IETF TRUST 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
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
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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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----