draft-ietf-eai-rfc5336bis-16.txt   rfc6531.txt 
Network Working Group J. Yao Internet Engineering Task Force (IETF) J. Yao
Internet-Draft W. Mao Request for Comments: 6531 W. Mao
Obsoletes: 5336 (if approved) CNNIC Obsoletes: 5336 CNNIC
Intended status: Standards Track November 10, 2011 Category: Standards Track February 2012
Expires: May 13, 2012 ISSN: 2070-1721
SMTP Extension for Internationalized Email SMTP Extension for Internationalized Email
draft-ietf-eai-rfc5336bis-16.txt
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. This specification replaces RFC 5336. information.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on May 13, 2012. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6531.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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skipping to change at page 3, line 7 skipping to change at page 2, line 14
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Changes Made to Other Specifications . . . . . . . . . . . 5 1.2. Changes Made to Other Specifications . . . . . . . . . . . 3
2. Overview of Operation . . . . . . . . . . . . . . . . . . . . 5 2. Overview of Operation . . . . . . . . . . . . . . . . . . . . 4
3. Mail Transport-Level Protocol . . . . . . . . . . . . . . . . 5 3. Mail Transport-Level Protocol . . . . . . . . . . . . . . . . 4
3.1. Framework for the Internationalization Extension . . . . . 5 3.1. Framework for the Internationalization Extension . . . . . 4
3.2. The UTF8SMTPbis Extension . . . . . . . . . . . . . . . . 6 3.2. The SMTPUTF8 Extension . . . . . . . . . . . . . . . . . . 5
3.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 7 3.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 7
3.4. MAIL Command Parameter Usage . . . . . . . . . . . . . . . 9 3.4. MAIL Command Parameter Usage . . . . . . . . . . . . . . . 8
3.5. Non-ASCII addresses and Reply-codes . . . . . . . . . . . 9 3.5. Non-ASCII Addresses and Reply-Codes . . . . . . . . . . . 9
3.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 10 3.6. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 9
3.7. Additional ESMTP Changes and Clarifications . . . . . . . 11 3.7. Additional ESMTP Changes and Clarifications . . . . . . . 10
3.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 11 3.7.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 10
3.7.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 11 3.7.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 10
3.7.3. Trace Information . . . . . . . . . . . . . . . . . . 11 3.7.3. Trace Information . . . . . . . . . . . . . . . . . . 11
3.7.4. UTF-8 Strings in Replies . . . . . . . . . . . . . . . 12 3.7.4. UTF-8 Strings in Replies . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
4.1. SMTP Service Extensions Registry . . . . . . . . . . . . . 14 4.1. SMTP Service Extensions Registry . . . . . . . . . . . . . 13
4.2. SMTP Enhanced Status Code Registry . . . . . . . . . . . . 14 4.2. SMTP Enhanced Status Code Registry . . . . . . . . . . . . 13
4.3. WITH protocol types sub-registry of the Mail 4.3. WITH Protocol Types Sub-Registry of the Mail
Transmission Types Registry . . . . . . . . . . . . . . . 15 Transmission Types Registry . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
7. Change History . . . . . . . . . . . . . . . . . . . . . . . . 17 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. draft-yao-eai-rfc5336bis: Version 00 . . . . . . . . . . . 17 7.1. Normative References . . . . . . . . . . . . . . . . . . . 16
7.2. draft-ietf-eai-rfc5336bis: Version 00 . . . . . . . . . . 17 7.2. Informative References . . . . . . . . . . . . . . . . . . 18
7.3. draft-ietf-eai-rfc5336bis: Version 01 . . . . . . . . . . 17
7.4. draft-ietf-eai-rfc5336bis: Version 02 . . . . . . . . . . 17
7.5. draft-ietf-eai-rfc5336bis: Version 03 . . . . . . . . . . 18
7.6. draft-ietf-eai-rfc5336bis: Version 04 . . . . . . . . . . 18
7.7. draft-ietf-eai-rfc5336bis: Version 05 . . . . . . . . . . 18
7.8. draft-ietf-eai-rfc5336bis: Version 06 . . . . . . . . . . 18
7.9. draft-ietf-eai-rfc5336bis: Version 07 . . . . . . . . . . 18
7.10. draft-ietf-eai-rfc5336bis: Version 08 . . . . . . . . . . 18
7.11. draft-ietf-eai-rfc5336bis: Version 09 . . . . . . . . . . 18
7.12. draft-ietf-eai-rfc5336bis: Version 10 . . . . . . . . . . 18
7.13. draft-ietf-eai-rfc5336bis: Version 11 . . . . . . . . . . 18
7.14. draft-ietf-eai-rfc5336bis: Version 12 . . . . . . . . . . 19
7.15. draft-ietf-eai-rfc5336bis: Version 13 . . . . . . . . . . 19
7.16. draft-ietf-eai-rfc5336bis: Version 14 . . . . . . . . . . 19
7.17. draft-ietf-eai-rfc5336bis: Version 15 . . . . . . . . . . 19
7.18. draft-ietf-eai-rfc5336bis: Version 16 . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
The document defines a Simple Mail Transfer Protocol [RFC5321] The document defines a Simple Mail Transfer Protocol [RFC5321]
extension so servers can advertise the ability to accept and process extension so servers can advertise the ability to accept and process
internationalized email addresses (see section 1.1), and internationalized email addresses (see Section 1.1) and
internationalized email headers [RFC5335bis]. internationalized email headers [RFC6532].
An extended overview of the extension model for internationalized An extended overview of the extension model for internationalized
email addresses and the email header appears in [RFC4952bis], email addresses and the email header appears in RFC 6530 [RFC6530],
referred to as "the framework document" in this specification. A referred to as "the framework document" in this specification. A
thorough understanding of the information in that document and in the thorough understanding of the information in that document and in the
base Internet email specifications [RFC5321] [RFC5322] is necessary base Internet email specifications [RFC5321] [RFC5322] is necessary
to understand and implement this specification. to understand and implement this specification.
[[anchor1: Note in Draft and to RFC Editor: The keyword represented
in this document by "UTF8SMTPbis" (and in the XML source by
"UTF8SMTPbis") is a placeholder. The actual keyword will need to be
assigned after document approval by a process to be worked out
between the responsible AD, WG co-chairs, and IANA. The assigned
keyword should be substituted here. This paragraph should be removed
before RFC publication.]]
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
The terms "UTF-8 string" or "UTF-8 character" are used to refer to The terms "UTF-8 string" or "UTF-8 character" are used to refer to
Unicode characters, which may or may not be members of the ASCII Unicode characters, which may or may not be members of the ASCII
subset, encoded in UTF-8. All other specialized terms used in this subset, in UTF-8 [RFC3629], a standard Unicode Encoding Form. All
specification are defined in the framework document or in the base other specialized terms used in this specification are defined in the
Internet email specifications. In particular, the terms "ASCII framework document or in the base Internet email specifications. In
address", "internationalized email address", "non-ASCII address", particular, the terms "ASCII address", "internationalized email
"UTF8SMTPbis", "internationalized message", and "message" are used in address", "non-ASCII address", "SMTPUTF8", "internationalized
this document according to the definitions in the framework document. message", and "message" are used in this document according to the
definitions in the framework document [RFC6530].
Non-ASCII characters or strings referred in this document MUST be Strings referred to in this document, including ASCII strings, MUST
expressed in UTF-8, a standard Unicode Encoding Form. be expressed in UTF-8.
This specification uses Augmented BNF (ABNF) rules [RFC5234]. Some This specification uses Augmented BNF (ABNF) rules [RFC5234]. Some
basic rules in this document are identified in Section 3.3 as being basic rules in this document are identified in Section 3.3 as being
defined (under the same names) in [RFC5234], [RFC5321], [RFC5890] or defined (under the same names) in RFC 5234 [RFC5234], RFC 5321
[RFC5335bis]. [RFC5321], RFC 5890 [RFC5890], or RFC 6532 [RFC6532].
1.2. Changes Made to Other Specifications 1.2. Changes Made to Other Specifications
This specification extends some syntax rules defined in RFC 5321 and This specification extends some syntax rules defined in RFC 5321 and
permits internationalized email addresses in the envelope, but it permits internationalized email addresses in the envelope and in
does not modify RFC 5321. It permits data formats defined in trace fields, but it does not modify RFC 5321. It permits data
[RFC5335bis], but it does not modify RFC 5322. It does require that formats defined in RFC 6532 [RFC6532], but it does not modify RFC
the 8BITMIME extension [RFC6152] be announced by the UTF8SMTPbis- 5322. It does require that the 8BITMIME extension [RFC6152] be
aware SMTP server and used with "BODY=8BMITMIME" by the UTF8SMTPbis- announced by the SMTPUTF8-aware SMTP server and used with
aware SMTP client, but it does not modify the 8BITMIME specification "BODY=8BITMIME" by the SMTPUTF8-aware SMTP client, but it does not
in any way. modify the 8BITMIME specification in any way.
This specification replaces an earlier, experimental, approach to the This specification replaces an earlier, experimental, approach to the
same problem [RFC5336]. Section 6 of [RFC4952bis] describes the same problem [RFC5336]. Section 6 of RFC 6530 [RFC6530] describes
changes in approach between [RFC5336] and this specification. Anyone the changes in approach between RFC 5336 [RFC5336] and this
trying to convert an implementation from the experimental specification. Anyone trying to convert an implementation from the
specification to the specification in this document will need to experimental specification to the specification in this document will
review those changes carefully. need to review those changes carefully.
2. Overview of Operation 2. Overview of Operation
This document specifies an element of the email internationalization This document specifies an element of the email internationalization
work, specifically the definition of an SMTP extension for work, specifically the definition of an SMTP extension for
internationalized email. The extension is identified with the token internationalized email. The extension is identified with the token
"UTF8SMTPbis". "SMTPUTF8".
The internationalized email headers specification [RFC5335bis] The internationalized email headers specification [RFC6532] provides
provides the details of email header features enabled by this the details of email header features enabled by this extension.
extension
3. Mail Transport-Level Protocol 3. Mail Transport-Level Protocol
3.1. Framework for the Internationalization Extension 3.1. Framework for the Internationalization Extension
The following service extension is defined: The following service extension is defined:
1. The name of the SMTP service extension is "Internationalized 1. The name of the SMTP service extension is "Internationalized
Email". Email".
2. The EHLO keyword value associated with this extension is 2. The EHLO keyword value associated with this extension is
"UTF8SMTPbis". "SMTPUTF8".
3. No parameter values are defined for this EHLO keyword value. In 3. No parameter values are defined for this EHLO keyword value. In
order to permit future (although unanticipated) extensions, the order to permit future (although unanticipated) extensions, the
EHLO response MUST NOT contain any parameters for this keyword. EHLO response MUST NOT contain any parameters for this keyword.
The UTF8SMTPbis-aware SMTP client MUST ignore any parameters if The SMTPUTF8-aware SMTP client MUST ignore any parameters if
they appear for this keyword; that is, the UTF8SMTPbis-aware they appear for this keyword; that is, the SMTPUTF8-aware SMTP
SMTP client MUST behave as if the parameters do not appear. If client MUST behave as if the parameters do not appear. If an
an SMTP server includes UTF8SMTPbis in its EHLO response, it SMTP server includes SMTPUTF8 in its EHLO response, it MUST be
MUST be fully compliant with this version of this specification. fully compliant with this version of this specification.
4. One OPTIONAL parameter "UTF8SMTPbis" is added to the MAIL 4. One OPTIONAL parameter, SMTPUTF8, is added to the MAIL command.
command. The parameter has no value. If this parameter is set The parameter does not accept a value. If this parameter is set
in the MAIL command, it indicates that the SMTP client is in the MAIL command, it indicates that the SMTP client is
UTF8SMTPbis-aware and asserts that the envelope includes the SMTPUTF8-aware. Its presence also asserts that the envelope
non-ASCII address or the message being sent is internationalized includes the non-ASCII address, the message being sent is an
message or the message being sent needs the UTF8SMTPbis support. internationalized message, or the message being sent needs the
5. The maximum length of a MAIL command line is increased by 13 SMTPUTF8 support.
characters by the possible addition of the UTF8SMTPbis
parameter. [[anchor5: RFC Editor: the number '13' will be 5. The maximum length of a MAIL command line is increased by 10
replaced by the new number (2 spaces + length of the new keyword characters to accommodate the possible addition of the SMTPUTF8
supposed to replace "UTF8SMTPbis").]] parameter.
6. One OPTIONAL parameter "UTF8SMTPbis" is added to the VRFY and
EXPN commands. The parameter UTF8SMTPbis has no value. The 6. One OPTIONAL parameter, SMTPUTF8, is added to the VERIFY (VRFY)
parameter indicates that the SMTP client can accept Unicode and EXPAND (EXPN) commands. The SMTPUTF8 parameter does not
characters in UTF-8 encoding in replies from the VRFY and EXPN accept a value. The parameter indicates that the SMTP client
commands. can accept Unicode characters in UTF-8 encoding in replies from
the VRFY and EXPN commands.
7. No additional SMTP verbs are defined by this extension. 7. No additional SMTP verbs are defined by this extension.
8. Servers offering this extension MUST provide support for, and 8. Servers offering this extension MUST provide support for, and
announce, the 8BITMIME extension [RFC6152]. announce, the 8BITMIME extension [RFC6152].
9. The reverse-path and forward-path of the SMTP MAIL and RCPT 9. The reverse-path and forward-path of the SMTP MAIL and RCPT
commands are extended to allow Unicode characters encoded in commands are extended to allow Unicode characters encoded in
UTF-8 in mailbox names (addresses). UTF-8 in mailbox names (addresses).
10. The mail message body is extended as specified in [RFC5335bis].
11. The UTF8SMTPbis extension is valid on the submission port
[RFC4409]. It may also be used with LMTP [RFC2033]. When these
protocols are used, their use should be reflected in trace field
WITH keywords as appropriate [RFC3848].
3.2. The UTF8SMTPbis Extension 10. The mail message body is extended as specified in RFC 6532
[RFC6532].
An SMTP server that announces this UTF8SMTPbis extension MUST be 11. The SMTPUTF8 extension is valid on the submission port
prepared to accept a UTF-8 string [RFC3629] in any position in which [RFC6409]. It may also be used with the Local Mail Transfer
RFC 5321 specifies that a <mailbox> can appear. Although the Protocol (LMTP) [RFC2033]. When these protocols are used, their
characters in the <local-part> are permitted to contain non-ASCII use should be reflected in the trace field WITH keywords as
characters, actual parsing of the <local-part>, and the delimiters appropriate [RFC3848].
used, are unchanged from the base email specification [RFC5321]. Any
domain name to be looked up in the DNS MUST conform to and be
processed as specified for IDNA [RFC5890]. When doing lookups, the
UTF8SMTPbis-aware SMTP client or server MUST either use a Unicode
aware DNS library, or transform the internationalized domain name to
the form of A-label as described in [RFC5890].
An SMTP client that receives the UTF8SMTPbis extension keyword in 3.2. The SMTPUTF8 Extension
An SMTP server that announces the SMTPUTF8 extension MUST be prepared
to accept a UTF-8 string [RFC3629] in any position in which RFC 5321
specifies that a <mailbox> can appear. Although the characters in
the <local-part> are permitted to contain non-ASCII characters, the
actual parsing of the <local-part> and the delimiters used are
unchanged from the base email specification [RFC5321]. Any domain
name to be looked up in the DNS MUST conform to and be processed as
specified for Internationalizing Domain Names in Applications (IDNA)
[RFC5890]. When doing lookups, the SMTPUTF8-aware SMTP client or
server MUST either use a Unicode-aware DNS library, or transform the
internationalized domain name to A-label form (i.e., a fully-
qualified domain name that contains one or more A-labels but no
U-labels) as specified in RFC 5890 [RFC5890].
An SMTP client that receives the SMTPUTF8 extension keyword in
response to the EHLO command MAY transmit mailbox names within SMTP response to the EHLO command MAY transmit mailbox names within SMTP
commands as internationalized strings in UTF-8 form. It MAY send a commands as internationalized strings in UTF-8 form. It MAY send a
UTF-8 header [RFC5335bis] (which may also include mailbox names in UTF-8 header [RFC6532] (which may also include mailbox names in
UTF-8). It MAY transmit the domain parts of mailbox names within UTF-8). It MAY transmit the domain parts of mailbox names within
SMTP commands or the message header as A-labels or U-labels SMTP commands or the message header as A-labels or U-labels
[RFC5890]. The presence of the SMTPUTF8 extension does not change
the server-relaying behaviors described in RFC 5321.
[RFC5890]. The presence of the UTF8SMTPbis extension does not change If the SMTPUTF8 SMTP extension is not offered by the SMTP server, the
RFC 5321 server relaying behaviors. SMTPUTF8-aware SMTP client MUST NOT transmit an internationalized
email address and MUST NOT transmit a mail message containing
internationalized mail headers as described in RFC 6532 [RFC6532] at
any level within its MIME structure [RFC2045]. (For this paragraph,
the internationalized domain name in A-label form as specified in
IDNA definitions [RFC5890] is not considered to be
"internationalized".) Instead, if an SMTPUTF8-aware SMTP client
(sender) attempts to transfer an internationalized message and
encounters an SMTP server that does not support the extension, the
best action for it to take depends on other conditions. In
particular:
If the UTF8SMTPbis SMTP extension is not offered by the SMTP server, o If it is a Message Submission Agent (MSA) [RFC6409] [RFC5598], it
the UTF8SMTPbis-aware SMTP client MUST NOT transmit an MAY choose its own way to deal with this scenario using the wide
internationalized email address and MUST NOT transmit a mail message discretion for changing addresses or otherwise fixing up and
containing internationalized mail headers as described in transforming messages allowed by RFC 6409. As long as the
[RFC5335bis] at any level within its MIME structure [RFC2045]. (For resulting message conforms to the requirements of RFC 5321 (i.e.,
this paragraph, the internationalized domain name in the form of without the SMTPUTF8 extension), the details of that
A-labels as specified in IDNA definitions [RFC5890] is not considered transformation are outside the scope of this document.
to be "internationalized".) Instead, if a UTF8SMTPbis-aware SMTP
client (UTF8SMTPbis-aware SMTP sender) attempts to transfer an
internationalized message and encounters an SMTP server that does not
support the extension, it MUST make one of the following three
choices and the priority order is 1, 2 and 3.
1. It MAY either reject the message during the SMTP transaction or o If it is not an MSA or is an MSA and does not choose to transform
accept the message and then generate and transmit a notification the message to one that does not require the SMTPUTF8 extension,
of non-deliverability. Such notification MUST be done as it SHOULD reject the message. As usual, this can be done either
specified in RFC 5321 [RFC5321], RFC 3464 [RFC3464], and the by generating an appropriate reply during the SMTP transaction or
internationalized delivery status and disposition notifications by accepting the message and then generating and transmitting a
specification [RFC5337bis]. non-delivery notification. If the latter choice is made, the
2. If and only if the UTF8SMTPbis-aware SMTP client (sender) is a notification process MUST conform to the requirements of RFC 5321,
Message Submission Agent ("MSA") [RFC4409] [RFC5598], it MAY RFC 3464 [RFC3464], and RFC 6533 [RFC6533].
choose its own way to deal with this scenario according to the
provisions of [RFC4409] or its future versions. But the detailed
specification of this process and its results are outside the
scope of this document.
3. It MAY find an alternate route to the destination that permits
UTF8SMTPbis. That route MAY be discovered by trying alternate
Mail eXchanger (MX) hosts (using preference rules as specified in
RFC 5321) or using other means available to the UTF8SMTPbis-aware
SMTP client.
This document applies when a UTF8SMTPbis-aware SMTP client or server o As specified in Section 2.2.3 of RFC 5321, an SMTP client with
supports the UTF8SMTPbis extension. For all other cases, and for additional information and/or knowledge of special circumstances
addresses and messages that do not require a UTF8SMTPbis extension, MAY choose to requeue the message and try later and/or try an
UTF8SMTPbis-aware SMTP clients and servers do not change the behavior alternate MX host as specified in that section.
specified in [RFC5321].
If a UTF8SMTPbis-aware SMTP server advertises the Delivery Status This document applies when an SMTPUTF8-aware SMTP client or server
Notification (DSN) [RFC3461] extension, it MUST implement supports the SMTPUTF8 extension. For all other cases, and for
[RFC5337bis]. addresses and messages that do not require an SMTPUTF8 extension,
SMTPUTF8-aware SMTP clients and servers do not change the behavior
specified in RFC 5321 [RFC5321].
If an SMTPUTF8-aware SMTP server advertises the Delivery Status
Notification (DSN) [RFC3461] extension, it MUST implement RFC 6533
[RFC6533].
3.3. Extended Mailbox Address Syntax 3.3. Extended Mailbox Address Syntax
RFC 5321, section 4.1.2, defines the syntax of a <Mailbox> entirely RFC 5321, Section 4.1.2, defines the syntax of a <Mailbox> entirely
in terms of ASCII characters. This document extends <Mailbox> to add in terms of ASCII characters. This document extends <Mailbox> to add
support of non-ASCII characters. support of non-ASCII characters.
The key changes made by this specification include: The key changes made by this specification include:
o In order to update the <Mailbox> to support the internationalized
email address, the <Mailbox> ABNF rule will be imported from RFC o The <Mailbox> ABNF rule is imported from RFC 5321 and updated in
5321 directly, and other related rules are imported from RFC 5321, order to support the internationalized email address. Other
RFC 5234, RFC 5890 or RFC 5335bis, or are extended in this related rules are imported from RFC 5321, RFC 5234, RFC 5890, and
document. RFC 6532, or are extended in this document.
o Extend the definition of <sub-domain> to permit both the RFC 5321
definition and a UTF-8 string in a DNS label that is conforming o The definition of <sub-domain> is extended to permit both the RFC
5321 definition and a UTF-8 string in a DNS label that conforms
with IDNA definitions [RFC5890]. with IDNA definitions [RFC5890].
o Extend the definition of <atext> to permit both the RFC 5321
o The definition of <atext> is extended to permit both the RFC 5321
definition and a UTF-8 string. That string MUST NOT contain any definition and a UTF-8 string. That string MUST NOT contain any
of the ASCII graphics or controls characters. of the ASCII graphics or control characters.
The following ABNF rules imported from RFC 5321, section 4.1.2 are The following ABNF rules imported from RFC 5321, Section 4.1.2, are
updated directly or indirectly by this document: updated directly or indirectly by this document:
o <Mailbox> o <Mailbox>
o <Local-part> o <Local-part>
o <Dot-string> o <Dot-string>
o <Quoted-string> o <Quoted-string>
o <QcontentSMTP> o <QcontentSMTP>
o <Domain> o <Domain>
o <Atom> o <Atom>
The following ABNF rule will be imported from RFC 5335bis, section The following ABNF rule will be imported from RFC 6532, Section 3.1,
3.1 directly: directly:
o <UTF8-non-ascii>
The following ABNF rule will be imported from RFC 5234, appendix B.1 o <UTF8-non-ascii>
The following ABNF rule will be imported from RFC 5234, Appendix B.1,
directly: directly:
o <DQUOTE> o <DQUOTE>
The following ABNF rule will be imported from RFC 5890, section The following ABNF rule will be imported from RFC 5890, Section
2.3.2.1 directly: 2.3.2.1, directly:
o <U-label> o <U-label>
The following rules are extended in ABNF [RFC5234] as follows. The following rules are extended in ABNF [RFC5234] as follows.
sub-domain =/ U-label sub-domain =/ U-label
; extend the definition of sub-domain in RFC5321, section 4.1.2 ; extend the definition of sub-domain in RFC 5321, Section 4.1.2
atext =/ UTF8-non-ascii atext =/ UTF8-non-ascii
; extend the implicit definition of atext in ; extend the implicit definition of atext in
; RFC5321, Section 4.1.2, which ultimately points to ; RFC 5321, Section 4.1.2, which ultimately points to
; the actual definition in RFC5322, Section 3.2.3 ; the actual definition in RFC 5322, Section 3.2.3
qtextSMTP =/ UTF8-non-ascii qtextSMTP =/ UTF8-non-ascii
; extend the definition of qtextSMTP in RFC5321, section 4.1.2 ; extend the definition of qtextSMTP in RFC 5321, Section 4.1.2
esmtp-value =/ UTF8-non-ascii esmtp-value =/ UTF8-non-ascii
; extend the definition of esmtp-value in RFC5321, section 4.1.2 ; extend the definition of esmtp-value in RFC 5321, Section 4.1.2
3.4. MAIL Command Parameter Usage 3.4. MAIL Command Parameter Usage
If the envelope or message being sent requires the capabilities of If the envelope or message being sent requires the capabilities of
the UTF8SMTPbis extension, the UTF8SMTPbis-aware SMTP client MUST the SMTPUTF8 extension, the SMTPUTF8-aware SMTP client MUST supply
supply the UTF8SMTPbis parameter with the MAIL command. If this the SMTPUTF8 parameter with the MAIL command. If this parameter is
parameter is provided, it MUST have no value. If the UTF8SMTPbis- provided, it MUST not accept a value. If the SMTPUTF8-aware SMTP
aware SMTP client is aware that neither the envelope nor the message client is aware that neither the envelope nor the message being sent
being sent requires any of the UTF8SMTPbis extension capabilities, it requires any of the SMTPUTF8 extension capabilities, it SHOULD NOT
SHOULD NOT supply the UTF8SMTPbis parameter with the MAIL command. supply the SMTPUTF8 parameter with the MAIL command.
Because there is no guarantee that a next-hop SMTP server will Because there is no guarantee that a next-hop SMTP server will
support the UTF8SMTPbis extension, use of the UTF8SMTPbis extension support the SMTPUTF8 extension, use of the SMTPUTF8 extension always
always carries a risk of transmission failure. In fact, during the carries a risk of transmission failure. In fact, during the early
early stages of deployment for the UTF8SMTPbis extension, the risk stages of deployment for the SMTPUTF8 extension, the risk will be
will be quite high. Hence there is a distinct near-term advantage quite high. Hence, there is a distinct near-term advantage for
for ASCII-only messages to be sent without using this extension. The ASCII-only messages to be sent without using this extension. The
long-term advantage of casting ASCII [ASCII] characters(0x7f and long-term advantage of casting ASCII [ASCII] characters (0x7f and
below) as UTF-8 form is that it permits pure-Unicode environments. below) as UTF-8 form is that it permits pure-Unicode environments.
3.5. Non-ASCII addresses and Reply-codes 3.5. Non-ASCII Addresses and Reply-Codes
A UTF8SMTPbis-aware SMTP client MUST NOT send an internationalized An SMTPUTF8-aware SMTP client MUST NOT send an internationalized
message to an SMTP server that does not support UTF8SMTPbis. If the message to an SMTP server that does not support SMTPUTF8. If the
SMTP server does not support this option, then the UTF8SMTPbis-aware SMTP server does not support this option, then the SMTPUTF8-aware
SMTP client has three choices according to section 3.2 of this SMTP client has three choices according to Section 3.2 of this
specification. specification.
The three-digit Reply-codes used in this section are based on their The three-digit reply-codes used in this section are based on their
meanings as defined in RFC 5321. meanings as defined in RFC 5321.
When messages are rejected because the RCPT command requires an ASCII When messages are rejected because the RCPT command requires an ASCII
address, the reply-code 553 is returned with the meaning "mailbox address, the reply-code 553 is returned with the meaning "mailbox
name not allowed". When messages are rejected because the MAIL name not allowed". When messages are rejected because the MAIL
command requires an ASCII address, the reply-code 550 is returned command requires an ASCII address, the reply-code 550 is returned
with the meaning "mailbox unavailable". When the UTF8SMTPbis-aware with the meaning "mailbox unavailable". When the SMTPUTF8-aware SMTP
SMTP server supports enhanced mail system status codes [RFC3463], server supports enhanced mail system status codes [RFC3463], reply-
reply-code "X.6.7" [RFC5248] (see section 4)is used, meaning that code "X.6.7" [RFC5248] (see Section 4) is used, meaning "Non-ASCII
"non-ASCII addresses not permitted for that sender/recipient". addresses not permitted for that sender/recipient".
When messages are rejected for other reasons, the server follows the When messages are rejected for other reasons, the server follows the
model of the base email specifications in RFC 5321; this extension model of the base email specification in RFC 5321; this extension
does not change those circumstances or reply messages. does not change those circumstances or reply messages.
If a message is rejected after the final "." of the DATA command If a message is rejected after the final "." of the DATA command
because one or more recipient is unable to accept and process a because one or more recipients are unable to accept and process a
message with internationalized email headers, the reply-code "554" is message with internationalized email headers, the reply-code "554" is
used with the meaning "Transaction failed". If the UTF8SMTPbis-aware used with the meaning "Transaction failed". If the SMTPUTF8-aware
SMTP server supports enhanced mail system status codes [RFC3463], SMTP server supports enhanced mail system status codes [RFC3463],
reply code "X.6.9" [RFC5248] (see section 4) is used to indicate this reply code "X.6.9" [RFC5248] (see Section 4) is used to indicate this
condition, meaning that "UTF-8 header message can not be transmitted condition, meaning "UTF-8 header message cannot be transmitted to one
to one or more recipients, so the message MUST be rejected". or more recipients, so the message must be rejected".
The UTF8SMTPbis-aware SMTP servers are encouraged to detect that The SMTPUTF8-aware SMTP servers are encouraged to detect that
recipients can not accept internationalized messages and generate an recipients cannot accept internationalized messages and generate an
error after the RCPT command rather than waiting until after the DATA error after the RCPT command rather than waiting until after the DATA
command to issue an error. command to issue an error.
3.6. Body Parts and SMTP Extensions 3.6. Body Parts and SMTP Extensions
The MAIL command parameter UTF8SMTPbis asserts that a message is an The MAIL command parameter SMTPUTF8 asserts that a message is an
internationalized message or the message being sent needs the internationalized message or the message being sent needs the
UTF8SMTPbis support. There is still a chance that a message being SMTPUTF8 support. There is still a chance that a message being sent
sent via the MAIL command with the UTF8SMTPbis parameter is not an via the MAIL command with the SMTPUTF8 parameter is not an
internationalized message. A UTF8SMTPbis-aware SMTP client or server internationalized message. An SMTPUTF8-aware SMTP client or server
that requires accurate knowledge of whether a message is that requires accurate knowledge of whether a message is
internationalized needs to parse all message header fields and MIME internationalized needs to parse all message header fields and MIME
header fields [RFC2045] in the message body. However, this header fields [RFC2045] in the message body. However, this
specification does not require that the UTF8SMTPbis-aware SMTP client specification does not require that the SMTPUTF8-aware SMTP client or
or server inspects the message. server inspects the message.
Although this specification requires that UTF8SMTPbis-aware SMTP Although this specification requires that SMTPUTF8-aware SMTP servers
servers support the 8BITMIME extension [RFC6152] to ensure that support the 8BITMIME extension [RFC6152] to ensure that servers have
servers have adequate handling capability for 8-bit data, it does not adequate handling capability for 8-bit data, it does not require non-
require non-ASCII body parts in the MIME message in RFC 2045. The ASCII body parts in the MIME message as specified in RFC 2045. The
UTF8SMTPbis extension MAY be used with the BODY=8BITMIME parameter SMTPUTF8 extension MAY be used as follows (assuming it is appropriate
[RFC6152] if that is appropriate given the body content or, with the given the body content):
BODY=BINARYMIME parameter, if the SMTP server advertises BINARYMIME
[RFC3030] and that is appropriate. - with the BODY=8BITMIME parameter [RFC6152], or
- with the BODY=BINARYMIME parameter, if the SMTP server advertises
BINARYMIME [RFC3030].
3.7. Additional ESMTP Changes and Clarifications 3.7. Additional ESMTP Changes and Clarifications
The information carried in the mail transport process involves The information carried in the mail transport process involves
addresses ("mailboxes") and domain names in various contexts in addresses ("mailboxes") and domain names in various contexts in
addition to the MAIL and RCPT commands and extended alternatives to addition to the MAIL and RCPT commands and extended alternatives to
them. In general, the rule is that, when RFC 5321 specifies a them. In general, the rule is that, when RFC 5321 specifies a
mailbox, this SMTP extension requires UTF-8 form to be used for the mailbox, this SMTP extension requires UTF-8 form to be used for the
entire string. When RFC 5321 specifies a domain name, the entire string. When RFC 5321 specifies a domain name, the
internationalized domain name SHOULD be in the form of U-label if the internationalized domain name SHOULD be in U-label form if the
UTF8SMTPbis extension is supported; otherwise, it SHOULD be in the SMTPUTF8 extension is supported; otherwise, it SHOULD be in A-label
form of A-label. form.
The following subsections list and discuss all of the relevant cases. The following subsections list and discuss all of the relevant cases.
3.7.1. The Initial SMTP Exchange 3.7.1. The Initial SMTP Exchange
When an SMTP connection is opened, the SMTP server sends a "greeting" When an SMTP connection is opened, the SMTP server sends a "greeting"
response consisting of the 220 reply-code and some information. The response consisting of the 220 reply-code and some information. The
SMTP client then sends the EHLO command. Since the SMTP client SMTP client then sends the EHLO command. Since the SMTP client
cannot know whether the SMTP server supports UTF8SMTPbis until after cannot know whether the SMTP server supports SMTPUTF8 until after it
it receives the response from EHLO, the UTF8SMTPbis-aware SMTP client receives the response to the EHLO, the SMTPUTF8-aware SMTP client
MUST send only ASCII (LDH label or A-label [RFC5890] ) domains in the MUST send only ASCII (LDH label or A-label [RFC5890]) domains in the
EHLO command and that, if the UTF8SMTPbis-aware SMTP server provides EHLO command. If the SMTPUTF8-aware SMTP server provides domain
domain names in the EHLO response, they MUST be in the form of LDH names in the EHLO response, they MUST be in the form of LDH labels or
labels or A-labels. A-labels.
3.7.2. Mail eXchangers 3.7.2. Mail eXchangers
If multiple DNS MX records are used to specify multiple servers for a If multiple DNS MX records are used to specify multiple servers for a
domain in section 5 of [RFC5321], it is strongly advised that all or domain (as described in Section 5 of RFC 5321 [RFC5321]), it is
none of them SHOULD support the UTF8SMTPbis extension. Otherwise, strongly advised that all or none of them SHOULD support the SMTPUTF8
unexpected rejections can happen during temporary or permanent extension. Otherwise, unexpected rejections can happen during
failures, which users might perceive as serious reliability issues. temporary or permanent failures, which users might perceive as
serious reliability issues.
3.7.3. Trace Information 3.7.3. Trace Information
The trace information <Return-path-line>, <Time-stamp-line> and their The trace information <Return-path-line>, <Time-stamp-line>, and
related rules are defined in in section 4.4 of RFC 5321 [RFC5321]. their related rules are defined in Section 4.4 of RFC 5321 [RFC5321].
This document updates <Mailbox> and <Domain> to support non-ASCII This document updates <Mailbox> and <Domain> to support non-ASCII
characters. When the UTF8SMTPbis extension is used, the 'Reverse- characters. When the SMTPUTF8 extension is used, the 'Reverse-path'
path' clause of the Return-path-line may include an internationalized clause of the Return-path-line may include an internationalized
domain name that uses the U-label form; The 'Stamp' clause of the domain name that uses the U-label form. Also, the 'Stamp' clause of
Time-stamp-line may include an internationalized domain name that the Time-stamp-line may include an internationalized domain name that
uses the U-label form. uses the U-label form.
If the messages that include trace fields are sent by an UTF8SMTPbis- If the messages that include trace fields are sent by an SMTPUTF8-
aware SMTP client or relay server without the UTF8SMTPbis parameter aware SMTP client or relay server without the SMTPUTF8 parameter
at MAIL commands, trace field values must conform to RFC 5321 included in the MAIL commands, trace field values must conform to RFC
regardless of the SMTP server's capability. 5321 regardless of the SMTP server's capability.
When a UTF8SMTPbis-aware SMTP server adds a trace field to a message When an SMTPUTF8-aware SMTP server adds a trace field to a message
that was or will be transmitted with the UTF8SMTPbis parameter at that was or will be transmitted with the SMTPUTF8 parameter included
MAIL commands, that server SHOULD use the U-label form for in the MAIL commands, that server SHOULD use the U-label form for
internationalized domain names in that new trace field. internationalized domain names in the new trace field.
The protocol value of the 'WITH' clause when this extension is used The protocol value of the 'WITH' clause when this extension is used
is one of the UTF8SMTPbis values specified in the "IANA is one of the SMTPUTF8 values specified in the "IANA Considerations"
Considerations" section of this document. section of this document.
3.7.4. UTF-8 Strings in Replies 3.7.4. UTF-8 Strings in Replies
3.7.4.1. MAIL Command 3.7.4.1. MAIL Command
If an SMTP client follows this specification and sends any MAIL If an SMTP client follows this specification and sends any MAIL
commands containing the UTF8SMTPbis parameter, the UTF8SMTPbis-aware commands containing the SMTPUTF8 parameter, the SMTPUTF8-aware SMTP
SMTP server is permitted to use UTF-8 characters in the email address server is permitted to use UTF-8 characters in the email address
associated with 251 and 551 reply-codes, and the SMTP client MUST be associated with 251 and 551 reply-codes, and the SMTP client MUST be
able to accept and process them. If a given MAIL command does not able to accept and process them. If a given MAIL command does not
include the UTF8SMTPbis parameter, the UTF8SMTPbis-aware SMTP server include the SMTPUTF8 parameter, the SMTPUTF8-aware SMTP server MUST
MUST NOT return a 251 or 551 response containing a non-ASCII mailbox. NOT return a 251 or 551 response containing a non-ASCII mailbox.
Instead, it MUST transform such responses into 250 or 550 responses Instead, it MUST transform such responses into 250 or 550 responses
that do not contain non-ASCII addresses. that do not contain non-ASCII addresses.
3.7.4.2. VRFY and EXPN Commands and the UTF8SMTPbis Parameter 3.7.4.2. VRFY and EXPN Commands and the SMTPUTF8 Parameter
If the VRFY and EXPN commands are transmitted with the parameter If the SMTPUTF8 parameter is transmitted with the VRFY and EXPN
"UTF8SMTPbis", it indicates the SMTP client can accept UTF-8 strings commands, it indicates that the SMTP client can accept UTF-8 strings
in replies to those commands. This parameter for the VRFY and EXPN in replies to those commands. The parameter with the VRFY and EXPN
commands SHOULD only be used after the SMTP client sees the EHLO commands SHOULD only be used after the SMTP client sees the EHLO
response with the UTF8SMTPbis keyword. This allows the UTF8SMTPbis- response with the SMTPUTF8 keyword. This allows an SMTPUTF8-aware
aware SMTP server to use UTF-8 strings in mailbox names and full SMTP server to use UTF-8 strings in mailbox names and full names that
names that occur in replies without concern that the SMTP client occur in replies, without concern that the SMTP client might be
might be confused by them. An SMTP client that conforms to this confused by them. An SMTP client that conforms to this specification
specification MUST accept and correctly process replies from the VRFY MUST accept and correctly process replies to the VRFY and EXPN
and EXPN commands that contain UTF-8 strings. However, the commands that contain UTF-8 strings. However, an SMTPUTF8-aware SMTP
UTF8SMTPbis-aware SMTP server MUST NOT use UTF-8 strings in replies server MUST NOT use UTF-8 strings in replies if the SMTP client does
if the SMTP client does not specifically allow such replies by not specifically allow such replies by transmitting this parameter
transmitting this parameter. Most replies do not require that a with the VRFY and EXPN commands.
mailbox name be included in the returned text, and therefore UTF-8
string is not needed in them. Some replies, notably those resulting Most replies do not require that a mailbox name be included in the
from successful execution of the VRFY and EXPN commands, do include returned text, and therefore a UTF-8 string is not needed in them.
the mailbox. Some replies, notably those resulting from successful execution of
the VRFY and EXPN commands, do include the mailbox.
VERIFY (VRFY) and EXPAND (EXPN) command syntaxes are changed to: VERIFY (VRFY) and EXPAND (EXPN) command syntaxes are changed to:
vrfy = "VRFY" SP String vrfy = "VRFY" SP String
[ SP "UTF8SMTPbis" ] CRLF [ SP "SMTPUTF8" ] CRLF
; String may include Non-ASCII characters ; String may include Non-ASCII characters
expn = "EXPN" SP String expn = "EXPN" SP String
[ SP "UTF8SMTPbis" ] CRLF [ SP "SMTPUTF8" ] CRLF
; String may include Non-ASCII characters ; String may include Non-ASCII characters
The "UTF8SMTPbis" parameter does not have a value. If the reply to a The SMTPUTF8 parameter does not accept a value. If the reply to a
VERIFY (VRFY) or EXPAND (EXPN) command requires a UTF-8 string, but VRFY or EXPN command requires a UTF-8 string, but the SMTP client did
the SMTP client did not use the "UTF8SMTPbis" parameter, then the not use the SMTPUTF8 parameter, then the SMTPUTF8-aware SMTP server
UTF8SMTPbis-aware SMTP server MUST use either the reply-code 252 or MUST use either the reply-code 252 or 550. Reply-code 252, defined
550. Reply-code 252, defined in [RFC5321], means "Cannot VRFY user, in RFC 5321 [RFC5321], means "Cannot VRFY user, but will accept the
but will accept the message and attempt the delivery". Reply-code message and attempt the delivery". Reply-code 550, also defined in
550, also defined in [RFC5321], means "Requested action not taken: RFC 5321 [RFC5321], means "Requested action not taken: mailbox
mailbox unavailable". When the UTF8SMTPbis-aware SMTP server unavailable". When the SMTPUTF8-aware SMTP server supports enhanced
supports enhanced mail system status codes [RFC3463], the enhanced mail system status codes [RFC3463], the enhanced reply-code as
reply-code as specified below is used. Using the "UTF8SMTPbis" specified below is used. Using the SMTPUTF8 parameter with a VRFY or
parameter with a VERIFY (VRFY) or EXPAND (EXPN) command enables UTF-8 EXPN command enables UTF-8 replies for that command only.
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 <Mailbox> User Name <Mailbox>
; Mailbox is defined in section 3.3 of this document. ; Mailbox is defined in Section 3.3 of this document.
; User Name can contain non-ASCII characters. ; User Name can contain non-ASCII characters.
Mailbox Mailbox
; Mailbox is defined in section 3.3 of this document. ; Mailbox is defined in Section 3.3 of this document.
If the SMTP reply requires UTF-8 strings, but UTF-8 string is not If the SMTP reply requires UTF-8 strings, but a UTF-8 string is not
allowed in the reply, and the UTF8SMTPbis-aware SMTP server supports allowed in the reply, and the SMTPUTF8-aware SMTP server supports
enhanced mail system status codes [RFC3463], the enhanced reply-code enhanced mail system status codes [RFC3463], the enhanced reply-code
is "X.6.8" [RFC5248] (see section 4), meaning "A reply containing a is "X.6.8" [RFC5248] (see Section 4), meaning "A reply containing a
UTF-8 string is REQUIRED to show the mailbox name, but that form of UTF-8 string is required to show the mailbox name, but that form of
response is not permitted by the SMTP client". response is not permitted by the SMTP client".
If the SMTP client does not support the UTF8SMTPbis extension, but If the SMTP client does not support the SMTPUTF8 extension, but
receives a UTF-8 string in a reply, it may not be able to properly receives a UTF-8 string in a reply, it may not be able to properly
report the reply to the user, and some clients might mishandle that report the reply to the user, and some clients might mishandle that
reply. Internationalized messages in replies are only allowed in the reply. Internationalized messages in replies are only allowed in the
commands under the situations described above. commands under the situations described above.
Although UTF-8 form is needed to represent email addresses in Although UTF-8 strings are needed to represent email addresses in
responses under the rules specified in this section, this extension responses under the rules specified in this section, this extension
does not permit the use of UTF-8 string for any other purposes. does not permit the use of UTF-8 strings for any other purposes.
UTF8SMTPbis-aware SMTP servers MUST NOT include non-ASCII characters SMTPUTF8-aware SMTP servers MUST NOT include non-ASCII characters in
in replies except in the limited cases specifically permitted in this replies except in the limited cases specifically permitted in this
section. section.
4. IANA Considerations 4. IANA Considerations
4.1. SMTP Service Extensions Registry 4.1. SMTP Service Extensions Registry
IANA is requested to add a new value "UTF8SMTPbis" to the SMTP IANA has added a new value "SMTPUTF8" to the "SMTP Service Extension"
Service Extension Registry of the Mail Parameters registry, according registry of the "Mail Parameters" registry, according to the
to the following data: following data:
+-------------+---------------------------------+-----------+ +----------+---------------------------------+-----------+
| Keywords | Description | Reference | | Keywords | Description | Reference |
+-------------+---------------------------------+-----------+ +----------+---------------------------------+-----------+
| UTF8SMTPbis | Internationalized email address | [RFCXXXX] | | SMTPUTF8 | Internationalized email address | [RFC6531] |
+-------------+---------------------------------+-----------+ +----------+---------------------------------+-----------+
4.2. SMTP Enhanced Status Code Registry 4.2. SMTP Enhanced Status Code Registry
The new code definitions in this document replace those that now The code definitions in this document replace those specified in RFC
appear in the SMTP Enhanced Status Code subregistry of the Mail 5336, following the guidance in Sections 3.5 and 3.7.4.2 of this
Parameters registry, following the guidance in Sections 3.5 and document, and based on RFC 5248 [RFC5248]. IANA has updated the
3.7.4.2 of this document, and being based on [RFC5248]. The "Simple Mail Transfer Protocol (SMTP) Enhanced Status Code Registry"
registration data is as follows: with the following data:
Code: X.6.7 Code: X.6.7
Sample Text: non-ASCII addresses not permitted Sample Text: Non-ASCII addresses not permitted for that
for that sender/recipient sender/recipient
Associated basic status code: 550, 553 Associated basic status code: 550, 553
Description: This indicates the reception of a MAIL or RCPT Description: This indicates the reception of a MAIL or RCPT command
command that non-ASCII addresses are not permitted that non-ASCII addresses are not permitted.
Defined: RFC XXXX (Standard track) Defined: RFC 6531 (Standards Track)
Submitter: Jiankang YAO Submitter: Jiankang YAO
Change controller: ima@ietf.org Change controller: ima@ietf.org
Code: X.6.8
Sample Text: UTF-8 string reply is required, Code: X.6.8
but not permitted by the SMTP client Sample Text: UTF-8 string reply is required, but not permitted by
the SMTP client
Associated basic status code: 252, 550, 553 Associated basic status code: 252, 550, 553
Description: This indicates that a reply containing a UTF-8 Description: This indicates that a reply containing a UTF-8 string
string is required to show the mailbox name, is required to show the mailbox name, but that form of
but that form of response is not response is not permitted by the SMTP client.
permitted by the SMTP client. Defined: RFC 6531 (Standards Track)
Defined: RFC XXXX (Standard track) Submitter: Jiankang YAO
Submitter: Jiankang YAO
Change controller: ima@ietf.org Change controller: ima@ietf.org
Code: X.6.9 Code: X.6.9
Sample Text: UTF-8 header message can not be transferred Sample Text: UTF-8 header message cannot be transferred to one or
to one or more recipient so the message more recipients, so the message must be rejected
must be rejected
Associated basic status code: 550 Associated basic status code: 550
Description: This indicates that transaction failed Description: This indicates that transaction failed after the
after the final "." of the DATA command. final "." of the DATA command.
Defined: RFC XXXX (Standard track) Defined: RFC 6531 (Standards Track)
Submitter: Jiankang YAO Submitter: Jiankang YAO
Change controller: ima@ietf.org Change controller: ima@ietf.org
Code: X.6.10 Code: X.6.10
Description: This is a duplicate of X.6.8 and Description: This is a duplicate of X.6.8 and is thus deprecated.
is thus deprecated.
4.3. WITH protocol types sub-registry of the Mail Transmission Types 4.3. WITH Protocol Types Sub-Registry of the Mail Transmission Types
Registry Registry
IANA is requested to update or add the following entries in the "Mail IANA has modified or added the following entries in the "WITH
Transmission Types" registry under the Mail Parameters registry. protocol types" sub-registry under the "Mail Transmission Types"
registry.
+-------------+---------------------------------+-------------------+ +--------------+------------------------------+---------------------+
| WITH | Description | Reference | | WITH | Description | Reference |
| protocol | | | | protocol | | |
| types | | | | types | | |
+-------------+---------------------------------+-------------------+ +--------------+------------------------------+---------------------+
| UTF8SMTP | ESMTP with UTF8SMTPbis | [RFCXXXX] | | UTF8SMTP | ESMTP with SMTPUTF8 | [RFC6531] |
| UTF8SMTPA | ESMTP with UTF8SMTPbis and SMTP | [RFC4954] | | UTF8SMTPA | ESMTP with SMTPUTF8 and AUTH | [RFC4954] [RFC6531] |
| | AUTH | [RFCXXXX] | | UTF8SMTPS | ESMTP with SMTPUTF8 and | [RFC3207] [RFC6531] |
| UTF8SMTPS | ESMTP with UTF8SMTPbis and | [RFC3207] | | | STARTTLS | |
| | STARTTLS | [RFCXXXX] | | UTF8SMTPSA | ESMTP with SMTPUTF8 and both | [RFC3207] [RFC4954] |
| UTF8SMTPSA | ESMTP with UTF8SMTPbis and both | [RFC3207] | | | STARTTLS and AUTH | [RFC6531] |
| | STARTTLS and SMTP AUTH | [RFC4954] | | UTF8LMTP | LMTP with SMTPUTF8 | [RFC6531] |
| | | [RFCXXXX] | | UTF8LMTPA | LMTP with SMTPUTF8 and AUTH | [RFC4954] [RFC6531] |
| UTF8LMTP | LMTP with UTF8SMTPbis | [RFCXXXX] | | UTF8LMTPS | LMTP with SMTPUTF8 and | [RFC3207] [RFC6531] |
| UTF8LMTPA | LMTP with UTF8SMTPbis and SMTP | [RFC4954] | | | STARTTLS | |
| | AUTH | [RFCXXXX] | | UTF8LMTPSA | LMTP with SMTPUTF8 and both | [RFC3207] [RFC4954] |
| UTF8LMTPS | LMTP with UTF8SMTPbis and | [RFC3207] | | | STARTTLS and AUTH | [RFC6531] |
| | STARTTLS | [RFCXXXX] | +--------------+------------------------------+---------------------+
| UTF8LMTPSA | LMTP with UTF8SMTPbis and both | [RFC3207] |
| | STARTTLS and LMTP AUTH | [RFC4954] |
| | | [RFCXXXX] |
+-------------+---------------------------------+-------------------+
5. Security Considerations 5. Security Considerations
The extended security considerations discussion in the framework The extended security considerations discussion in the framework
document [RFC4952bis] will apply here. document [RFC6530] applies here.
More security considerations are discussed below: More security considerations are discussed below:
Beyond the use inside the email global system (in SMTP envelopes and Beyond the use inside the email global system (in SMTP envelopes and
message headers), internationalized email addresses will also show up message headers), internationalized email addresses will also show up
inside other cases, in particular: inside other cases, in particular:
o the logging systems of SMTP transactions and other logs to monitor o the logging systems of SMTP transactions and other logs to monitor
the email systems; the email systems;
o the trouble ticket systems used by Security Teams to manage
o the trouble ticket systems used by security teams to manage
security incidents, when an email address is involved; security incidents, when an email address is involved;
In order to avoid problems that could cause loss of data, this will In order to avoid problems that could cause loss of data, this will
likely require extending these systems to support full UTF-8, or to likely require extending these systems to support full UTF-8, or
require to provide an adequate mechanisms for mapping non-ASCII require providing an adequate mechanism for mapping non-ASCII strings
strings to ASCII. to ASCII.
Another security aspect to be considered is related to the ability by Another security aspect to be considered is related to the ability by
security team members to quickly understand, read and identify email security team members to quickly understand, read, and identify email
addresses from the logs, when they are tracking an incident. addresses from the logs, when they are tracking an incident.
Mechanisms to automatically and quickly provide the origin or Mechanisms to automatically and quickly provide the origin or
ownership of an internationalized email address SHALL be implemented ownership of an internationalized email address SHALL be implemented
for use also by log readers which cannot read easily non-ASCII for use by log readers that cannot easily read non-ASCII information.
information.
The SMTP commands VRFY and EXPN are sometimes used in SMTP The SMTP commands VRFY and EXPN are sometimes used in SMTP
transactions where there is no message to transfer (by tools used to transactions where there is no message to transfer (by tools used to
take automated actions in case potential spam messages are take automated actions in case potential spam messages are
identified). RFC 5321 section 3.5 and 7.3 give some detailed identified). Sections 3.5 and 7.3 of RFC 5321 give detailed
description of use and possible behaviours. Implementation of descriptions of use and possible behaviors. Implementation of
internationalized addresses can affect also logs and actions by these internationalized addresses can also affect logs and actions by these
tools. tools.
6. Acknowledgements 6. Acknowledgements
This document revised the [RFC5336]document based on the Email This document revises RFC 5336 [RFC5336] based on the result of the
Address Internationalization (EAI) WG's discussion result. Many EAI Email Address Internationalization (EAI) working group's discussion.
WG members did some tests and implementations to move this document Many EAI working group members did tests and implementations to move
to the Standard Track document. Significant comments and suggestions this document to the Standards Track. Significant comments and
were received from Xiaodong LEE, Nai-Wen Hsu, Yangwoo KO, Yoshiro suggestions were received from Xiaodong LEE, Nai-Wen HSU, Yangwoo KO,
YONEYA, and other members of the JET team and were incorporated into Yoshiro YONEYA, and other members of JET and were incorporated into
the specification. Additional important comments and suggestions, the specification. Additional important comments and suggestions,
and often specific text, were contributed by many members of the WG and often specific text, were contributed by many members of the
and design team. Those contributions include material from John C working group and design team. Those contributions include material
Klensin, Charles Lindsey, Dave Crocker, Harald Tveit Alvestrand, from John C. Klensin, Charles Lindsey, Dave Crocker, Harald Tveit
Marcos Sanz, Chris Newman, Martin Duerst, Edmon Chung, Tony Finch, Alvestrand, Marcos Sanz, Chris Newman, Martin Duerst, Edmon Chung,
Kari Hurtta, Randall Gellens, Frank Ellermann, Alexey Melnikov, Pete Tony Finch, Kari Hurtta, Randall Gellens, Frank Ellermann, Alexey
Resnick, S. Moonesamy, Soobok Lee, Shawn Steele, Alfred Hoenes, Melnikov, Pete Resnick, S. Moonesamy, Soobok Lee, Shawn Steele,
Miguel Garcia, Magnus Westerlund, Joseph Yee and Lars Eggert. Of Alfred Hoenes, Miguel Garcia, Magnus Westerlund, Joseph Yee, and Lars
course, none of the individuals are necessarily responsible for the Eggert. Of course, none of the individuals are necessarily
combination of ideas represented here. responsible for the combination of ideas represented here.
Thanks a lot to Dave Crocker for his comments and helping of ABNF Thanks a lot to Dave Crocker for his comments and helping with ABNF
refinement. refinement.
7. Change History 7. References
[[anchor15: RFC Editor: Please remove this section.]]
7.1. draft-yao-eai-rfc5336bis: Version 00
Applied errata suggested by Alfred Hoenes.
7.2. draft-ietf-eai-rfc5336bis: Version 00
Applied the changes suggested by the EAI new charter.
7.3. draft-ietf-eai-rfc5336bis: Version 01
Applied the changes suggested by 78 IETF EAI meeting.
7.4. draft-ietf-eai-rfc5336bis: Version 02
remove the appendix since rfc4952bis has added this material
improve the text
remove the text about no body parameter
7.5. draft-ietf-eai-rfc5336bis: Version 03
improve the text
7.6. draft-ietf-eai-rfc5336bis: Version 04
update the abstract
improve the text
7.7. draft-ietf-eai-rfc5336bis: Version 05
improve the text based on AD and Co-chairs
7.8. draft-ietf-eai-rfc5336bis: Version 06
update the iana consideration
7.9. draft-ietf-eai-rfc5336bis: Version 07
improve the iana consideration
7.10. draft-ietf-eai-rfc5336bis: Version 08
improve the texts
add the mail parameter
add the new section about mail command parameter usage
update the security consideration
7.11. draft-ietf-eai-rfc5336bis: Version 09
improve the texts
7.12. draft-ietf-eai-rfc5336bis: Version 10
refine the ABNF definitions
improve the texts
7.13. draft-ietf-eai-rfc5336bis: Version 11
remove the update of RFC5321 and RFC5322
change the title from "SMTP Extension for Internationalized Email
Address" to "SMTP Extension for Internationalized Email" based on
Ernie's comment
the trace field of section 3.7.3 is updated to reflect the WG's
conclusion
improve the texts
7.14. draft-ietf-eai-rfc5336bis: Version 12
Update according to Chris Newman's comments
improve the texts
7.15. draft-ietf-eai-rfc5336bis: Version 13
Update the esmpt-value syntax according to Chris Newman's comments
improve the texts
7.16. draft-ietf-eai-rfc5336bis: Version 14
improve the texts
7.17. draft-ietf-eai-rfc5336bis: Version 15
improve the texts
updates based on IESG members' comments
7.18. draft-ietf-eai-rfc5336bis: Version 16
improve the texts
8. References
8.1. 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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service [RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)", Extension for Delivery Status Notifications (DSNs)",
skipping to change at page 20, line 18 skipping to change at page 17, line 22
[RFC3464] Moore, K. and G. Vaudreuil, "An Extensible Message Format [RFC3464] Moore, K. and G. Vaudreuil, "An Extensible Message Format
for Delivery Status Notifications", RFC 3464, for Delivery Status Notifications", RFC 3464,
January 2003. January 2003.
[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.
[RFC3848] Newman, C., "ESMTP and LMTP Transmission Types [RFC3848] Newman, C., "ESMTP and LMTP Transmission Types
Registration", RFC 3848, July 2004. Registration", RFC 3848, July 2004.
[RFC4409] Gellens, R. and J. Klensin, "Message Submission for Mail",
RFC 4409, April 2006.
[RFC4952bis]
Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", I-D rfc4952bis, September 2011.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5248] Hansen , T. and J. Klensin, "A Registry for SMTP Enhanced [RFC5248] Hansen, T. and J. Klensin, "A Registry for SMTP Enhanced
Mail System Status Codes", RFC 5248, June 2008. Mail System Status Codes", RFC 5248, June 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008. October 2008.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008. October 2008.
[RFC5335bis]
Abel, Y. and S. Steel, "Internationalized Email Headers",
I-D rfc5335bis, March 2011.
[RFC5337bis]
Hansen, T., Ed., Newman, C., and A. Melnikov, Ed.,
"Internationalized Delivery Status and Disposition
Notifications", I-D 5337bis, October 2010.
[RFC5890] Klensin, J., "Internationalizing Domain Names in [RFC5890] Klensin, J., "Internationalizing Domain Names in
Applications (IDNA definitions)", RFC 5890, June 2010. Applications (IDNA definitions)", RFC 5890, June 2010.
[RFC6152] Klensin, J., Freed, N., Rose, M., and D. Crocker, "SMTP [RFC6152] Klensin, J., Freed, N., Rose, M., and D. Crocker, "SMTP
Service Extension for 8-bit MIME Transport", STD 71, Service Extension for 8-bit MIME Transport", STD 71,
RFC 6152, March 2011. RFC 6152, March 2011.
8.2. Informative References [RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail",
STD 72, RFC 6409, November 2011.
[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 6530, February 2012.
[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized
Email Headers", RFC 6532, February 2012.
[RFC6533] Hansen, T., Ed., Newman, C., and A. Melnikov, Ed.,
"Internationalized Delivery Status and Disposition
Notifications", RFC RFC6533, February 2012.
7.2. Informative References
[RFC2033] Myers, J., "Local Mail Transfer Protocol", RFC 2033, [RFC2033] Myers, J., "Local Mail Transfer Protocol", RFC 2033,
October 1996. October 1996.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, November 1996.
[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,
skipping to change at page 21, line 36 skipping to change at page 18, line 36
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
July 2009. July 2009.
Authors' Addresses Authors' Addresses
Jiankang YAO Jiankang YAO
CNNIC CNNIC
No.4 South 4th Street, Zhongguancun No.4 South 4th Street, Zhongguancun
Beijing Beijing
China
Phone: +86 10 58813007 Phone: +86 10 58813007
Email: yaojk@cnnic.cn EMail: yaojk@cnnic.cn
Wei MAO Wei MAO
CNNIC CNNIC
No.4 South 4th Street, Zhongguancun No.4 South 4th Street, Zhongguancun
Beijing Beijing
China
Phone: +86 10 58812230 Phone: +86 10 58812230
Email: maowei_ietf@cnnic.cn EMail: maowei_ietf@cnnic.cn
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