draft-ietf-eai-smtpext-09.txt   draft-ietf-eai-smtpext-10.txt 
Network Working Group J. Yao, Ed. Network Working Group J. Yao, Ed.
Internet-Draft W. Mao, Ed. Internet-Draft W. Mao, Ed.
Updates: RFC4952 CNNIC Updates: RFC4952 CNNIC
(if approved) November 17, 2007 (if approved) January 8, 2008
Intended status: Experimental Intended status: Experimental
Expires: May 20, 2008 Expires: July 11, 2008
SMTP extension for internationalized email address SMTP extension for internationalized email address
draft-ietf-eai-smtpext-09.txt draft-ietf-eai-smtpext-10.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware 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 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. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
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This Internet-Draft will expire on May 20, 2008. This Internet-Draft will expire on July 11, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
Abstract Abstract
This document specifies an SMTP extension for transport and delivery This document specifies an SMTP extension for transport and delivery
of email messages with internationalized email addresses or header of email messages with internationalized email addresses or header
information. Communication with systems that do not implement this information. Communication with systems that do not implement this
specification is specified in another document. specification is specified in another document.
Table of Contents Table of Contents
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1.1. Role of this specification . . . . . . . . . . . . . . . . 3 1.1. Role of this specification . . . . . . . . . . . . . . . . 3
1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 3 1.2. Proposal Context . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 4 2. Mail Transport-level Protocol . . . . . . . . . . . . . . . . 4
2.1. Framework for the Internationalization Extension . . . . . 4 2.1. Framework for the Internationalization Extension . . . . . 4
2.2. The UTF8SMTP Extension . . . . . . . . . . . . . . . . . . 5 2.2. The UTF8SMTP Extension . . . . . . . . . . . . . . . . . . 5
2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 6 2.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 6
2.4. The ALT-ADDRESS Parameter . . . . . . . . . . . . . . . . 8 2.4. The ALT-ADDRESS Parameter . . . . . . . . . . . . . . . . 8
2.5. ALT-ADDRESS Parameter Usage and Response Codes . . . . . . 9 2.5. ALT-ADDRESS Parameter Usage and Response Codes . . . . . . 9
2.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 10 2.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 10
2.7. Additional ESMTP Changes and Clarifications . . . . . . . 10 2.7. Additional ESMTP Changes and Clarifications . . . . . . . 11
2.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 11 2.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 11
2.7.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 11 2.7.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 11
2.7.3. Trace Information . . . . . . . . . . . . . . . . . . 11 2.7.3. Trace Information . . . . . . . . . . . . . . . . . . 11
2.7.4. UTF-8 Strings in Replies . . . . . . . . . . . . . . . 12 2.7.4. UTF-8 Strings in Replies . . . . . . . . . . . . . . . 12
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
4. Security Considerations . . . . . . . . . . . . . . . . . . . 14 4. Security Considerations . . . . . . . . . . . . . . . . . . . 15
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
6. Change History . . . . . . . . . . . . . . . . . . . . . . . . 15 6. Change History . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1. draft-ietf-eai-smtpext: Version 00 . . . . . . . . . . . . 15 6.1. draft-ietf-eai-smtpext: Version 00 . . . . . . . . . . . . 15
6.2. draft-ietf-eai-smtpext: Version 01 . . . . . . . . . . . . 15 6.2. draft-ietf-eai-smtpext: Version 01 . . . . . . . . . . . . 16
6.3. draft-ietf-eai-smtpext: Version 02 . . . . . . . . . . . . 15 6.3. draft-ietf-eai-smtpext: Version 02 . . . . . . . . . . . . 16
6.4. draft-ietf-eai-smtpext: Version 03 . . . . . . . . . . . . 15 6.4. draft-ietf-eai-smtpext: Version 03 . . . . . . . . . . . . 16
6.5. draft-ietf-eai-smtpext: Version 04 . . . . . . . . . . . . 16 6.5. draft-ietf-eai-smtpext: Version 04 . . . . . . . . . . . . 16
6.6. draft-ietf-eai-smtpext: Version 05 . . . . . . . . . . . . 16 6.6. draft-ietf-eai-smtpext: Version 05 . . . . . . . . . . . . 16
6.7. draft-ietf-eai-smtpext: Version 06 . . . . . . . . . . . . 16 6.7. draft-ietf-eai-smtpext: Version 06 . . . . . . . . . . . . 16
6.8. draft-ietf-eai-smtpext: Version 07 . . . . . . . . . . . . 16 6.8. draft-ietf-eai-smtpext: Version 07 . . . . . . . . . . . . 17
6.9. draft-ietf-eai-smtpext: Version 08 . . . . . . . . . . . . 16 6.9. draft-ietf-eai-smtpext: Version 08 . . . . . . . . . . . . 17
6.10. draft-ietf-eai-smtpext: Version 09 . . . . . . . . . . . . 16 6.10. draft-ietf-eai-smtpext: Version 09 . . . . . . . . . . . . 17
6.11. draft-ietf-eai-smtpext: Version 10 . . . . . . . . . . . . 17
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Normative References . . . . . . . . . . . . . . . . . . . 17 7.1. Normative References . . . . . . . . . . . . . . . . . . . 17
7.2. Informative References . . . . . . . . . . . . . . . . . . 18 7.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. Material Updating RFC 4952 . . . . . . . . . . . . . 18 Appendix A. Material Updating RFC 4952 . . . . . . . . . . . . . 19
A.1. Conventional Message and Internationalized Message . . . . 19 A.1. Conventional Message and Internationalized Message . . . . 19
A.2. LMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 A.2. LMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 19 A.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 20
A.4. Implementation Advice . . . . . . . . . . . . . . . . . . 19 A.4. Implementation Advice . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 A.5. Applicability of SMTP Extension to Additional Uses . . . . 20
Intellectual Property and Copyright Statements . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 22
1. Introduction 1. Introduction
An internationalized email address includes two parts, the local part An internationalized email address includes two parts, the local part
and the domain part. The ways email addresses are used by protocols and the domain part. The ways email addresses are used by protocols
are different from the ways domain names are used. The most critical are different from the ways domain names are used. The most critical
difference is that emails are delivered through a chain of clients difference is that emails are delivered through a chain of clients
and servers while domain names are resolved by name servers looking and servers while domain names are resolved by name servers looking
up those names in their own tables. In addition to this, the up those names in their own tables. In addition to this, the
extended email transport protocol [RFC2821] provides a negotiation extended email transport protocol [RFC2821] provides a negotiation
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UTF-8 header [EAI-utf8header] (which may also include mailbox names UTF-8 header [EAI-utf8header] (which may also include mailbox names
in UTF-8). It MAY transmit the domain parts of mailbox names within in UTF-8). It MAY transmit the domain parts of mailbox names within
SMTP commands or the message header in either the form of ACE labels SMTP commands or the message header in either the form of ACE labels
as specified in IDNA [RFC3490] or as UTF-8 strings. All labels in as specified in IDNA [RFC3490] or as UTF-8 strings. All labels in
domain parts of mailbox names which are IDNs (either UTF-8 or ACE domain parts of mailbox names which are IDNs (either UTF-8 or ACE
strings) MUST be valid. If the original client submits a message to strings) MUST be valid. If the original client submits a message to
a Message Submission Server ("MSA") [RFC4409], it is the a Message Submission Server ("MSA") [RFC4409], it is the
responsibility of the MSA that all domain labels are valid; otherwise responsibility of the MSA that all domain labels are valid; otherwise
it is the original client's responsibility. The presence of the it is the original client's responsibility. The presence of the
UTF8SMTP extension does not change the requirement of RFC 2821 that UTF8SMTP extension does not change the requirement of RFC 2821 that
servers relaying mail MUST not attempt to parse, evaluate, or servers relaying mail MUST NOT attempt to parse, evaluate, or
transform the local part in any way. transform the local part in any way.
If the UTF8SMTP SMTP extension is not offered by the Server, the SMTP If the UTF8SMTP SMTP extension is not offered by the Server, the SMTP
client MUST NOT transmit an internationalized address and MUST NOT client MUST NOT transmit an internationalized address and MUST NOT
transmit a mail message containing internationalized mail headers as transmit a mail message containing internationalized mail headers as
described in [EAI-utf8header] at any level within its MIME structure. described in [EAI-utf8header] at any level within its MIME structure.
Instead, if an SMTP client (SMTP sender) attempts to transfer a Instead, if an SMTP client (SMTP sender) attempts to transfer a
internationalized message and encounters a server that does not internationalized message and encounters a server that does not
support the extension, it MUST make one of the following four support the extension, it MUST make one of the following four
choices: choices:
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preference rules as specified in RFC 2821) or using other means preference rules as specified in RFC 2821) or using other means
available to the SMTP-sender. available to the SMTP-sender.
4. If and only if ASCII addresses are available for all addresses 4. If and only if ASCII addresses are available for all addresses
that appear in the return path and the specific forward paths that appear in the return path and the specific forward paths
being attempted, downgrade the message to an all-ASCII form as being attempted, downgrade the message to an all-ASCII form as
specified in [EAI-downgrading]. An ASCII address is considered specified in [EAI-downgrading]. An ASCII address is considered
to be "available" for a particular address if the original to be "available" for a particular address if the original
address in the envelope is in ASCII or if an ALT-ADDRESS address in the envelope is in ASCII or if an ALT-ADDRESS
parameter is specified for a UTF8SMTP address. parameter is specified for a UTF8SMTP address.
The difference between "choice 1" and "choice 4" is that "choice 1"
is constrained by Message Submission [RFC4409], while "choice 4" is
constrained by [EAI-downgrading].
2.3. Extended Mailbox Address Syntax 2.3. Extended Mailbox Address Syntax
RFC 2821, section 4.1.2, defines the syntax of a mailbox entirely in RFC 2821, section 4.1.2, defines the syntax of a mailbox entirely in
terms of ASCII characters, using the production for a mailbox and terms of ASCII characters, using the production for a mailbox and
those on which it depends. those on which it depends.
The key changes made by this specification are, informally, to The key changes made by this specification are, informally, to
o Change the definition of "sub-domain" to permit either the o Change the definition of "sub-domain" to permit either the
definition above or a UTF-8 string representing a DNS label that definition above or a UTF-8 string representing a DNS label that
is conformant with IDNA [RFC3490]. is conformant with IDNA [RFC3490].
o Change the definition of "Atom" to permit either the definition 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 above or a UTF-8 string. That string MUST NOT contain any of the
ASCII characters (either graphics or controls) that are not ASCII characters (either graphics or controls) that are not
permitted in "atext"; it is otherwise unrestricted. permitted in "atext"; it is otherwise unrestricted.
According to the description above, the syntax of an According to the description above, the syntax of an
internationalized email mailbox name (address) is defined in ABNF internationalized email mailbox name (address) is defined in ABNF
[RFC4234] as [RFC4234] as
uMailbox = uLocal-part "@" uDomain uMailbox = uLocal-part "@" uDomain
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2.4. The ALT-ADDRESS Parameter 2.4. The ALT-ADDRESS Parameter
If the UTF8SMTP extension is offered, the syntax of the SMTP MAIL and If the UTF8SMTP extension is offered, the syntax of the SMTP MAIL and
RCPT commands is extended to support the optional esmtp-keyword "ALT- RCPT commands is extended to support the optional esmtp-keyword "ALT-
ADDRESS". That keyword specifies an alternate all-ASCII address ADDRESS". That keyword specifies an alternate all-ASCII address
which may be used when downgrading. If the ALT-ADDRESS esmtp-keyword which may be used when downgrading. If the ALT-ADDRESS esmtp-keyword
is used, it MUST have an associated esmtp-value (ALT-ADDRESS-esmtp- is used, it MUST have an associated esmtp-value (ALT-ADDRESS-esmtp-
value, which is defined below). value, which is defined below).
While it may be tempting to consider ALT-ADDRESS as a general-purpose
second-chance address, such behavior is not defined here. Instead,
in this specification ALT-ADDRESS only has meaning when the
associated primary address is non-ASCII and the message is
downgraded. This restriction allows for future extension of the
specification even though no such extensions are currently
anticipated.
Based on the definition of mail-parameters in [RFC2821], the ALT- Based on the definition of mail-parameters in [RFC2821], the ALT-
ADDRESS parameter usage in the commands of "MAIL" and "RCPT" is ADDRESS parameter usage in the commands of "MAIL" and "RCPT" is
defined as follows. The following definitions are given in the same defined as follows. The following definitions are given in the same
format as used in RFC 2821. format as used in RFC 2821.
"MAIL FROM:" ("<>" / uReverse-path) [ SP Mail-parameters ] CRLF "MAIL FROM:" ("<>" / uReverse-path) [ SP Mail-parameters ] CRLF
; Update the MAIL command in RFC 2821, section 4.1.1.2. ; Update the MAIL command in RFC 2821, section 4.1.1.2.
; A new parameter defined by the ABNF non-terminal ; A new parameter defined by the ABNF non-terminal
; <ALT-ADDRESS-parameter> is added. It complies ; <ALT-ADDRESS-parameter> is added. It complies
; with the syntax specified for <esmtp-param> in RFC 2821. ; with the syntax specified for <esmtp-param> in RFC 2821.
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The ALT-ADDRESS-parameter MUST NOT appear more than once in any MAIL 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 or RCPT command. ALT-ADDRESS-esmtp-value MUST be an all-ASCII email
address before xtext encoding. address before xtext encoding.
2.5. ALT-ADDRESS Parameter Usage and Response Codes 2.5. ALT-ADDRESS Parameter Usage and Response Codes
An "internationalized message" as defined in the appendix of this An "internationalized message" as defined in the appendix of this
specification MUST NOT be sent to an SMTP server that does not specification MUST NOT be sent to an SMTP server that does not
support UTF8SMTP. Such a message MAY be rejected by a server if it support UTF8SMTP. Such a message MAY be rejected by a server if it
lacks one or more ALT-ADDRESSes as discussed in Section 2.2 of this lacks ALT-ADDRESSes as discussed in Section 2.2 of this
specification. specification.
The three-digit reply codes used in this section are consistent with The three-digit reply codes used in this section are consistent with
their meanings as defined in RFC 2821. their meanings as defined in RFC 2821.
When messages are rejected because the RCPT command requires an ALT- When messages are rejected because the RCPT command requires an ALT-
ADDRESS, the response code 553 is used with the meaning "mailbox name ADDRESS, the response code 553 is used with the meaning "mailbox name
not allowed". When messages are rejected for other reasons, such as not allowed". When messages are rejected for other reasons, such as
the MAIL command requiring an ALT-ADDRESS, the response code 550 is the MAIL command requiring an ALT-ADDRESS, the response code 550 is
used with the meaning "mailbox unavailable". If enhanced mail system used with the meaning "mailbox unavailable". When the server
status codes [RFC3463] are used, the response code should be "5.6.x" supports enhanced mail system status codes [RFC3463], response code
[SMTP-codes], meaning that "The ALT-ADDRESS is required but not "5.6.x" [SMTP-codes] is used, meaning that "The ALT-ADDRESS is
specified". required but not specified".
If the response code is issued after the final "." of the DATA If the response code is issued after the final "." of the DATA
command, the response code "554" is used with the meaning command, the response code "554" is used with the meaning
"Transaction failed". If enhanced mail system status codes [RFC3463] "Transaction failed". When the server supports enhanced mail system
are used, the response code should be "5.6.z" [SMTP-codes], meaning status codes [RFC3463], response code "5.6.z" [SMTP-codes] is used,
that "UTF8SMTP downgrade failed". meaning that "UTF8SMTP downgrade failed".
[[anchor7: RFC Editor: please insert the proper error codes for [[anchor7: RFC Editor: please insert the proper error codes for
"5.6.x" and "5.6.z" after IANA has made the relevant assignments.]] "5.6.x" and "5.6.z" after IANA has made the relevant assignments.]]
2.6. Body Parts and SMTP Extensions 2.6. Body Parts and SMTP Extensions
Since there is no ESMTP parameter which tells whether the message is There is no ESMTP parameter to assert that a message is an
an internationalized message, an SMTP server that requires accurate internationalized message. An SMTP server that requires accurate
knowledge of whether a message is internationalized is required to knowledge of whether a message is internationalized is required to
parse all message header fields and MIME header fields in the message parse all message header fields and MIME header fields in the message
body. While this specification requires that servers support the body.
8BITMIME extension [RFC1652] to ensure that servers have adequate
handling capability for 8-bit data and to avoid a number of complex While this specification requires that servers support the 8BITMIME
encoding problems, the use of internationalized addresses obviously extension [RFC1652] to ensure that servers have adequate handling
does not require non-ASCII body parts in the MIME message. The capability for 8-bit data and to avoid a number of complex encoding
UTF8SMTP extension MAY be used with the BODY=8BITMIME parameter if problems, the use of internationalized addresses obviously does not
that is appropriate given the body content or, if the server require non-ASCII body parts in the MIME message. The UTF8SMTP
advertises BINARYMIME [RFC3030] and the BODY=BINARYMIME is extension MAY be used with the BODY=8BITMIME parameter if that is
appropriate, with the BODY=BINARYMIME parameter. appropriate given the body content or, if the server advertises
BINARYMIME [RFC3030] and the BODY=BINARYMIME is appropriate, with the
BODY=BINARYMIME parameter.
Assuming that the server advertises UTF8SMTP and 8BITMIME, and Assuming that the server advertises UTF8SMTP and 8BITMIME, and
receives at least one non-ASCII address, with or without ALT-ADDRESS, receives at least one non-ASCII address, with or without ALT-ADDRESS,
the precise interpretation of "No 'Body' parameter", "BODY= the precise interpretation of "No 'Body' parameter", "BODY=8BITMIME",
8BITMIME", and "BODY= BINARYMIME" in the MAIL command is: and "BODY=BINARYMIME" in the MAIL command is:
1. If there is no "Body" parameter, the header contains UTF-8 1. If there is no "Body" parameter, the header contains UTF-8
characters but all the body parts are in ASCII (possibly as the characters but all the body parts are in ASCII (possibly as the
result of a Content-transfer-encoding). result of a Content-transfer-encoding).
2. If a BODY=8BITMIME parameter is present, the header contains 2. If a BODY=8BITMIME parameter is present, the header contains
UTF-8 characters and some or all of the body parts contain 8-bit UTF-8 characters and some or all of the body parts contain 8-bit
line-oriented data. line-oriented data.
3. If a BODY=BINARYMIME parameter is present, the header contains 3. If a BODY=BINARYMIME parameter is present, the header contains
UTF-8 characters and some or all body parts contain binary data UTF-8 characters and some or all body parts contain binary data
without restriction as to line lengths or delimiters. without restriction as to line lengths or delimiters.
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the MAIL and RCPT commands and extended alternatives to them. In the MAIL and RCPT commands and extended alternatives to them. In
general, the rule is that, when RFC 2821 specifies a mailbox, this general, the rule is that, when RFC 2821 specifies a mailbox, this
specification expects UTF-8 to be used for the entire string; when 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 RFC 2821 specifies a domain name, the name SHOULD be in the form of
ACE labels if its raw form is non-ASCII. ACE labels if its raw form is non-ASCII.
The following subsections list and discuss all of the relevant cases. The following subsections list and discuss all of the relevant cases.
2.7.1. The Initial SMTP Exchange 2.7.1. The Initial SMTP Exchange
When an SMTP or ESMTP connection is opened, the server normally sends When an SMTP connection is opened, the server normally sends a
a "greeting" response consisting of the '220' reply code and some "greeting" response consisting of the '220' reply code and some
information. The client then sends the EHLO command. Since the information. The client then sends the EHLO command. Since the
client cannot know whether the server supports UTF8SMTP until after client cannot know whether the server supports UTF8SMTP until after
it receives the response from EHLO, any domain names that appear in 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, 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. i.e., internationalized ones MUST be in the form of ACE labels.
2.7.2. Mail eXchangers 2.7.2. Mail eXchangers
Organizations often authorize multiple servers to accept mail Organizations often authorize multiple servers to accept mail
addressed to them. For example, the organization may itself operate addressed to them. For example, the organization may itself operate
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more than one server accepts mail for the domain-part of a mailbox, more than one server accepts mail for the domain-part of a mailbox,
it is strongly advised that either all or none of them support the it is strongly advised that either all or none of them support the
UTF8SMTP extension. Otherwise, surprising downgrades can happen UTF8SMTP extension. Otherwise, surprising downgrades can happen
during temporary failures, which is not a good thing. during temporary failures, which is not a good thing.
2.7.3. Trace Information 2.7.3. Trace Information
When an SMTP server receives a message for delivery or further When an SMTP server receives a message for delivery or further
processing, it MUST insert trace ("time stamp" or "Received") processing, it MUST insert trace ("time stamp" or "Received")
information at the beginning of the message content. "Time stamp" or information at the beginning of the message content. "Time stamp" or
"Received" appears in the form of "Received: lines". The most "Received" appears in the form of "Received:" lines. The most
important use of Received: lines is for debugging mail faults. When important use of Received: lines is for debugging mail faults. When
the delivery SMTP server makes the "final delivery" of a message, it the delivery SMTP server makes the "final delivery" of a message, it
inserts a return-path line at the beginning of the mail data. The inserts a return-path line at the beginning of the mail data. The
primary purpose of the Return-path is to designate the address to primary purpose of the Return-path is to designate the address to
which messages indicating non-delivery or other mail system failures which messages indicating non-delivery or other mail system failures
are to be sent. For the trace information, this memo updates the are to be sent. For the trace information, this memo updates the
time stamp line and the return path line [RFC2821] formally defined time stamp line and the return path line [RFC2821] formally defined
as follows: as follows:
uReturn-path-line = "Return-Path:" FWS uReverse-path <CRLF> uReturn-path-line = "Return-Path:" FWS uReverse-path <CRLF>
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; 2.3, respectively, of this document ; 2.3, respectively, of this document
[[anchor11: Note: The FOR parameter has been changed to match the [[anchor11: Note: The FOR parameter has been changed to match the
definition in RFC2821bis, permitting only one address in the For definition in RFC2821bis, permitting only one address in the For
clause. The group working on that document reached mailing list clause. The group working on that document reached mailing list
consensus that the syntax in RFC 2821 that permitted more than one consensus that the syntax in RFC 2821 that permitted more than one
address was simply a mistake.]] address was simply a mistake.]]
Except in the 'uFor' and 'uReverse-path' line where non-ASCII domain Except in the 'uFor' and 'uReverse-path' line where non-ASCII domain
names may be used, internationalized domain names in Received fields names may be used, internationalized domain names in Received fields
MUST be transmitted in the form of ACE labels. The protocol value of MUST be transmitted in the form of ACE labels. The protocol value of
the WITH clause is UTF8SMTP when this extension is used. More the WITH clause when this extension is used is one of the UTF8SMTP
information is in the "IANA Considerations" section of this values specified in the "IANA Considerations" section of this
specification. document.
2.7.4. UTF-8 Strings in Replies 2.7.4. UTF-8 Strings in Replies
2.7.4.1. MAIL and RCPT Commands 2.7.4.1. MAIL and RCPT Commands
If the client issues the RCPT command containing non-ASCII If the client issues the RCPT command containing non-ASCII
characters, the SMTP server is permitted to use UTF-8 characters in characters, the SMTP server is permitted to use UTF-8 characters in
the email address associated with 251 and 551 response codes. the email address associated with 251 and 551 response codes.
If an SMTP client follows this specification and sends any RCPT If an SMTP client follows this specification and sends any RCPT
commands containing non-ASCII addresses, it MUST be able to accept commands containing non-ASCII addresses, it MUST be able to accept
and process 251 or 551 replies containing UTF-8 email addresses. If and process 251 or 551 replies containing UTF-8 email addresses. If
a given RCPT command does not include a non-ASCII envelope address, a given RCPT command does not include a non-ASCII envelope address,
the server MUST not return a 251 or 551 response containing a non- the server MUST NOT return a 251 or 551 response containing a non-
ASCII mailbox. Instead, it MUST transform such responses into 250 or ASCII mailbox. Instead, it MUST transform such responses into 250 or
550 responses that do not contain addresses. 550 responses that do not contain addresses.
2.7.4.2. VRFY and EXPN Commands and the UTF8REPLY Parameter 2.7.4.2. VRFY and EXPN Commands and the UTF8REPLY Parameter
If the VRFY and EXPN commands are transmitted the optional parameter If the VRFY and EXPN commands are transmitted with the optional
"UTF8REPLY", it indicates the client can accept UTF-8 strings in parameter "UTF8REPLY", it indicates the client can accept UTF-8
replies from those commands. This allows the server to use UTF-8 strings in replies from those commands. This allows the server to
strings in mailbox names and full names which occur in replies use UTF-8 strings in mailbox names and full names which occur in
without concern that the client might be confused by them. An SMTP replies without concern that the client might be confused by them.
client that conforms to this specification MUST accept and correctly An SMTP client that conforms to this specification MUST accept and
process replies from the VRFY and EXPN commands that contain UTF-8 correctly process replies from the VRFY and EXPN commands that
strings. However the SMTP server MUST NOT use UTF-8 strings in contain UTF-8 strings. However the SMTP server MUST NOT use UTF-8
replies if the SMTP client does not specifically allow such replies strings in replies if the SMTP client does not specifically allow
by transmitting this parameter. Most replies do not require that a such replies by transmitting this parameter. Most replies do not
mailbox name be included in the returned text and therefore UTF-8 is require that a mailbox name be included in the returned text and
not needed in them. Some replies, notably those resulting from therefore UTF-8 is not needed in them. Some replies, notably those
successful execution of the VRFY and EXPN commands, do include the resulting from successful execution of the VRFY and EXPN commands, do
mailbox, making the provisions of this section important. include the mailbox, making the provisions of this section important.
VERIFY (VRFY) and EXPAND (EXPN)command syntaxes are changed to: VERIFY (VRFY) and EXPAND (EXPN)command syntaxes are changed to:
"VRFY" SP (uLocal-part / uMailbox) [SP "UTF8REPLY"] CRLF "VRFY" SP (uLocal-part / uMailbox) [SP "UTF8REPLY"] CRLF
; uLocal-part and uMailbox are defined in ; uLocal-part and uMailbox are defined in
: Section 2.3 of this document : Section 2.3 of this document
"EXPN" SP ( uLocal-part / uMailbox ) [ SP "UTF8REPLY" ] CRLF "EXPN" SP ( uLocal-part / uMailbox ) [ SP "UTF8REPLY" ] CRLF
; uLocal-part and uMailbox are defined in ; uLocal-part and uMailbox are defined in
; Section 2.3 of this document ; Section 2.3 of this document
There is no value associated with the "UTF8REPLY" parameter. If SMTP The "UTF8REPLY" parameter does not use a value. If the reply to a
reply requires UTF-8, but SMTP client does not use "UTF8REPLY" VERIFY (VRFY) or EXPAND (EXPN) command requires UTF-8, but the SMTP
parameter in the VERIFY (VRFY) and EXPAND (EXPN) commands, the client does not use the "UTF8REPLY" parameter, then either reply code
response code 252 is used, defined in [RFC2821], meaning "Cannot VRFY 252 or reply code 550 is used. Response code 252, defined in
user, but will accept the message and attempt the delivery". Also [RFC2821], means "Cannot VRFY user, but will accept the message and
response code 550 may be used, meaning "Requested action not taken: attempt the delivery". Response code 550, also defined in [RFC2821],
mailbox unavailable". If enhanced mail system status code [RFC3463] means "Requested action not taken: mailbox unavailable". When the
is used, response codes given on below is used. "UTF8REPLY" on the server supports enhanced mail system status codes [RFC3463], the
VERIFY (VRFY) or EXPAND (EXPN) commands enables UTF-8 for that enhanced response code as specified below is used. Using the
command only. "UTF8REPLY" parameter with a VERIFY (VRFY) or EXPAND (EXPN) command
enables UTF-8 replies for that command only.
If a normal success response (i.e., 250) is returned, the response If a normal success response (i.e., 250) is returned, the response
MAY include the full name of the user and MUST include the mailbox of 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: the user. It MUST be in either of the following forms:
User Name <uMailbox> User Name <uMailbox>
; uMailbox is defined in section 2.3 of this document ; uMailbox is defined in section 2.3 of this document
; User Name can contain non-ASCII characters. ; User Name can contain non-ASCII characters.
uMailbox uMailbox
; uMailbox is defined in section 2.3 of this document ; uMailbox is defined in section 2.3 of this document
If the SMTP reply requires UTF-8 strings, but UTF-8 is not allowed in If the SMTP reply requires UTF-8 strings, but UTF-8 is not allowed in
the reply, and enhanced mail system status codes [RFC3463] are used, the reply, and the server supports enhanced mail system status codes
the response code should be "5.6.y" or "2.6.y" [SMTP-codes], meaning [RFC3463], the enhanced response code is either "5.6.y" or "2.6.y"
that "A reply containing a UTF-8 string is required to show the [SMTP-codes], meaning "A reply containing a UTF-8 string is required
mailbox name, but that form of response is not permitted by the to show the mailbox name, but that form of response is not permitted
client.". by the client".
If the SMTP Client does not support the UTF8SMTP service extension, If the SMTP Client does not support the UTF8SMTP extension, but
but receives a the UTF-8 string in a reply, it may not be able to receives a UTF-8 string in a reply, it may not be able to properly
properly report the reply to the user or even crash. report the reply to the user, and some clients might crash.
Internationalized messages in replies are only allowed in the Internationalized messages in replies are only allowed in the
commands under the situations described above. Under any other commands under the situations described above. Under any other
circumstances, UTF-8 text MUST NOT appear in the reply. circumstances, UTF-8 text MUST NOT appear in the reply.
Although UTF-8 is needed to represent email addresses in responses Although UTF-8 is needed to represent email addresses in responses
under the rules specified in this section, this extension does not under the rules specified in this section, this extension does not
permit the use of UTF-8 for any other purposes. SMTP servers MUST permit the use of UTF-8 for any other purposes. SMTP servers MUST
NOT include non-ASCII characters in replies except in the limited NOT include non-ASCII characters in replies except in the limited
cases specifically permitted in this section. cases specifically permitted in this section.
[[anchor14: RFC Editor: please insert the proper error codes for
"5.6.y" and "2.6.y" after IANA has made the relevant assignments.]]
3. IANA Considerations 3. IANA Considerations
IANA is requested to add "UTF8SMTP" to the SMTP extensions registry IANA is requested to add "UTF8SMTP" to the SMTP extensions registry
with the entry pointing to this specification for its definition. with the entry pointing to this specification for its definition.
IANA is requested to assign the proper error codes for "5.6.x", IANA is requested to assign the proper error codes for "5.6.x",
"5.6.z", "5.6.y" and "2.6.y", following the guidance in Section 2.5, "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. and based on [SMTP-codes] and enter them in the appropriate registry.
The "Mail Transmission Types" registry is requested to be updated to The "Mail Transmission Types" registry is requested to be updated to
skipping to change at page 15, line 13 skipping to change at page 15, line 34
Much of the text in the initial version of this specification was Much of the text in the initial version of this specification was
derived or copied from [Klensin-emailaddr] with the permission of the derived or copied from [Klensin-emailaddr] with the permission of the
author. Significant comments and suggestions were received from author. Significant comments and suggestions were received from
Xiaodong LEE, Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other Xiaodong LEE, Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other
members of the JET team and were incorporated into the specification. members of the JET team and were incorporated into the specification.
Additional important comments and suggestions, and often specific Additional important comments and suggestions, and often specific
text, were contributed by many members of the WG and design team. text, were contributed by many members of the WG and design team.
Those contributions include material from John C Klensin, Charles Those contributions include material from John C Klensin, Charles
Lindsey, Dave Crocker, Harald Tveit Alvestrand, Marcos Sanz, Chris Lindsey, Dave Crocker, Harald Tveit Alvestrand, Marcos Sanz, Chris
Newman, Martin Duerst, Edmon Chung, Tony Finch, Kari Hurtta, Randall Newman, Martin Duerst, Edmon Chung, Tony Finch, Kari Hurtta, Randall
Gellens, Frank Ellermann, Alexey Melnikov, Pete Resnick, S.M., and Gellens, Frank Ellermann, Alexey Melnikov, Pete Resnick, S.
Soobok Lee. Of course, none of the individuals are necessarily Moonesamy, and Soobok Lee. Of course, none of the individuals are
responsible for the combination of ideas represented here. necessarily responsible for the combination of ideas represented
here.
6. Change History 6. Change History
[[anchor17: RFC Editor: Please remove this section.]] [[anchor18: RFC Editor: Please remove this section.]]
6.1. draft-ietf-eai-smtpext: Version 00 6.1. draft-ietf-eai-smtpext: Version 00
This version supercedes draft-yao-ima-smtpext-03.txt. It refines the This version supercedes draft-yao-ima-smtpext-03.txt. It refines the
ABNF definition of the internationalized email address. It ABNF definition of the internationalized email address. It
represents as the EAI working group document. represents as the EAI working group document.
6.2. draft-ietf-eai-smtpext: Version 01 6.2. draft-ietf-eai-smtpext: Version 01
o Upgraded to reflect discussions during IETF 66. o Upgraded to reflect discussions during IETF 66.
skipping to change at page 17, line 5 skipping to change at page 17, line 28
o Remove section 3.3 and section 4 o Remove section 3.3 and section 4
o Add the new term definitions of conventional message and o Add the new term definitions of conventional message and
international message in the appendix international message in the appendix
o Refine some texts according to suggestions from the EAI mailing o Refine some texts according to suggestions from the EAI mailing
list discussion during WG Last call list discussion during WG Last call
o Use the same reference for ASCII as RFC 2821. o Use the same reference for ASCII as RFC 2821.
o General editorial revision and cleanup, including extensive o General editorial revision and cleanup, including extensive
modifications to the XML to produce a version that has better odds modifications to the XML to produce a version that has better odds
of getting through the various checkers and validators. of getting through the various checkers and validators.
6.11. draft-ietf-eai-smtpext: Version 10
o Refine the text
o Add some text about "ALT-ADDRESS" in the section 2.4
o Add the appendix A.5
7. References 7. References
7.1. Normative References 7.1. Normative References
[ASCII] American National Standards Institute (formerly United [ASCII] American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for States of America Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, 1968. Information Interchange", ANSI X3.4-1968, 1968.
[EAI-dsn] Newman, C. and A. Melnikov, "SMTP extensions for DSNs", [EAI-dsn] Newman, C. and A. Melnikov, "SMTP extensions for DSNs",
draft-ietf-eai-dsn-03.txt (work in progress), draft-ietf-eai-dsn-03.txt (work in progress),
skipping to change at page 18, line 14 skipping to change at page 18, line 44
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, November 2003. 10646", RFC 3629, November 2003.
[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
[RFC4409] Gellens, R. and J. Klensin, "Message Submission for Mail", [RFC4409] Gellens, R. and J. Klensin, "Message Submission for Mail",
RFC 4409, April 2006. RFC 4409, April 2006.
[SMTP-codes]
Hansen , T. and J. KLensin, "A Registry for SMTP Enhanced
Mail System Status Codes",
draft-hansen-4468upd-mailesc-registry-02 (work in
progress), July 2007.
7.2. Informative References 7.2. Informative References
[EAI-downgrading] [EAI-downgrading]
YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading YONEYA, Y., Ed. and K. Fujiwara, Ed., "Downgrading
mechanism for Internationalized eMail Address", mechanism for Internationalized eMail Address",
draft-ietf-eai-downgrade-04 (work in progress), 7 2007. draft-ietf-eai-downgrade-04 (work in progress), 7 2007.
[Klensin-emailaddr] [Klensin-emailaddr]
Klensin, J., "Internationalization of Email Addresses", Klensin, J., "Internationalization of Email Addresses",
draft-klensin-emailaddr-i18n-03 (work in progress), draft-klensin-emailaddr-i18n-03 (work in progress),
skipping to change at page 18, line 39 skipping to change at page 19, line 30
[RFC3030] Vaudreuil, G., "SMTP Service Extensions for Transmission [RFC3030] Vaudreuil, G., "SMTP Service Extensions for Transmission
of Large and Binary MIME Messages", RFC 3030, of Large and Binary MIME Messages", RFC 3030,
December 2000. December 2000.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over [RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002. Transport Layer Security", RFC 3207, February 2002.
[RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension [RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension
for Authentication", RFC 4954, July 2007. 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 Appendix A. Material Updating RFC 4952
RFC 4952, the Overview and Framework document covering this set of RFC 4952, the Overview and Framework document covering this set of
extensions for internationalized email [EAI-framework], was completed extensions for internationalized email [EAI-framework], was completed
before this specification, which specifies a particular part of the before this specification, which specifies a particular part of the
protocol set. This appendix, which is normative, contains material protocol set. This appendix, which is normative, contains material
that would have been incorporated into RFC 4952 had it been delayed that would have been incorporated into RFC 4952 had it been delayed
until the work described in the rest of this specification was until the work described in the rest of this specification was
completed and that should be included in any update to RFC 4952. completed and that should be included in any update to RFC 4952.
skipping to change at page 20, line 5 skipping to change at page 20, line 38
local parts of those addresses MAY be made up of any ASCII local parts of those addresses MAY be made up of any ASCII
characters, although some of them MUST be quoted as specified there. characters, although some of them MUST be quoted as specified there.
It is notable in an internationalization context that there is a long It is notable in an internationalization context that there is a long
history on some systems of using overstruck ASCII characters (a history on some systems of using overstruck ASCII characters (a
character, a backspace, and another character) within a quoted string character, a backspace, and another character) within a quoted string
to approximate non-ASCII characters. This form of to approximate non-ASCII characters. This form of
internationalization SHOULD be phased out as this extension becomes internationalization SHOULD be phased out as this extension becomes
widely deployed but backward-compatibility considerations require widely deployed but backward-compatibility considerations require
that it continue to be supported. that it continue to be supported.
A.5. Applicability of SMTP Extension to Additional Uses
Among other protocol changes, the SMTP extension allows an optional
alternate address to be supplied with the MAIL and RCPT commands.
For the purposes of this set of specifications, this alternate
address only has meaning when the primary address contains UTF-8
characters and the message is downgraded. While it may be tempting
to consider the alternate address as a general-purpose second-chance
address, to be used whenever the primary address is rejected, such
behavior is not defined here. This restriction allows for future
extensions to be developed which create such a general-purpose
second-chance address, although no specific work on such an extension
is currently anticipated. Note that any such extension needs to
consider the question of what the RFC 974 sequencing rules mean when
different possible servers support different sets of ESMTP options
(or, in this case, addresses). The answer to this question may also
imply updates to [RFC2821].
Authors' Addresses Authors' Addresses
Jiankang YAO (editor) Jiankang YAO (editor)
CNNIC CNNIC
No.4 South 4th Street, Zhongguancun No.4 South 4th Street, Zhongguancun
Beijing Beijing
Phone: +86 10 58813007 Phone: +86 10 58813007
Email: yaojk@cnnic.cn Email: yaojk@cnnic.cn
Wei MAO (editor) Wei MAO (editor)
CNNIC CNNIC
No.4 South 4th Street, Zhongguancun No.4 South 4th Street, Zhongguancun
Beijing Beijing
Phone: +86 10 58813055 Phone: +86 10 58813055
Email: maowei_ietf@cnnic.cn Email: maowei_ietf@cnnic.cn
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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