One document matched: draft-ietf-eai-rfc5336bis-01.txt
Differences from draft-ietf-eai-rfc5336bis-00.txt
Network Working Group J. Yao, Ed.
Internet-Draft W. Mao, Ed.
Obsoletes: RFC5336 CNNIC
(if approved) August 11, 2010
Updates: RFC5321 and 5322
(if approved)
Intended status: Standards Track
Expires: February 12, 2011
SMTP Extension for Internationalized Email Address
draft-ietf-eai-rfc5336bis-01.txt
Abstract
This document specifies an SMTP extension for transport and delivery
of email messages with internationalized email addresses or header
information. Communication with systems that do not implement this
specification is specified in another document. This document
updates some syntaxes and rules defined in RFC 5321 and RFC 5322.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 12, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Role of This Specification . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Overview of Operation . . . . . . . . . . . . . . . . . . . . 5
3. Mail Transport-Level Protocol . . . . . . . . . . . . . . . . 5
3.1. Framework for the Internationalization Extension . . . . . 5
3.2. The UTF8SMTPbis Extension . . . . . . . . . . . . . . . . 6
3.3. Extended Mailbox Address Syntax . . . . . . . . . . . . . 7
3.4. UTF8 addresses and Response Codes . . . . . . . . . . . . 8
3.5. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 8
3.6. Additional ESMTP Changes and Clarifications . . . . . . . 9
3.6.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 9
3.6.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 10
3.6.3. Trace Information . . . . . . . . . . . . . . . . . . 10
3.6.4. UTF-8 Strings in Replies . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
7. Change History . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. draft-yao-eai-rfc5336bis: Version 00 . . . . . . . . . . . 15
7.2. draft-ietf-eai-rfc5336bis: Version 00 . . . . . . . . . . 15
7.3. draft-ietf-eai-rfc5336bis: Version 01 . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Additional Material . . . . . . . . . . . . . . . . . 17
A.1. Conventional Message and Internationalized Message . . . . 17
A.2. LMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
A.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 18
A.4. Implementation Advice . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
An internationalized email address includes two parts, the local part
and the domain part. The ways email addresses are used by protocols
are different from the ways domain names are used. The most critical
difference is that emails are delivered through a chain of clients
and servers, while domain names are resolved by name servers looking
up those names in their own tables. In addition to this, the Simple
Mail Transfer Protocol [RFC5321] provides a negotiation mechanism
about service extension with which clients can discover server
capabilities and make decisions for further processing. An extended
overview of the extension model for internationalized addresses and
headers appears in [RFC4952bis], referred to as "the framework
document" or just as "Framework" elsewhere in this specification.
This document specifies an SMTP extension to permit internationalized
email addresses in envelopes, and UNICODE characters (encoded in
UTF-8) [RFC3629] in headers.
1.1. Role of This Specification
The framework document specifies the requirements for, and describes
components of, full internationalization of electronic mail. A
thorough understanding of the information in that document and in the
base Internet email specifications [RFC5321] [RFC5322] is necessary
to understand and implement this specification.
This document specifies an element of the email internationalization
work, specifically the definition of an SMTP extension [RFC5321] for
internationalized email address transport delivery.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
The terms "conventional message" and "internationalized message" are
defined in an appendix to this specification. The terms "UTF-8
string" or "UTF-8 character" are used informally to refer to Unicode
characters encoded in UTF-8 [RFC3629]. All other specialized terms
used in this specification are defined in the framework document or
in the base Internet email specifications [RFC5321] [RFC5322]. In
particular, the terms "ASCII address", "internationalized email
address", "non-ASCII address", "i18mail address", "UTF8SMTPbis",
"message", and "mailing list" are used in this document according to
the definitions in the framework document.
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This specification defines only those Augmented BNF (ABNF) [RFC5234]
syntax rules that are different from those of the base email
specifications [RFC5321][RFC5322] and, where the earlier rules are
upgraded or extended, gives them new names. When the new rule is a
small modification to the older one, it is typically given a name
starting with "u". Rules that are undefined here may be found in the
base email specifications under the same names.
2. Overview of Operation
This specification describes an optional extension to the email
transport mechanism that permits non-ASCII [ASCII] characters in both
the envelope and header fields of messages, which are encoded with
UTF-8 [RFC3629] characters. The extension is identified with the
token "UTF8SMTPbis". In order to provide information that may be
needed in downgrading, an optional alternate ASCII address may be
needed if an SMTP client attempts to transfer an internationalized
message and encounters a server that does not support this extension.
The EAI UTF-8 header specification [RFC5335bis] provides the details
of how and where non-ASCII characters are permitted in the header
fields of messages. The context for this specification is described
in the framework document.
3. Mail Transport-Level Protocol
3.1. Framework for the Internationalization Extension
The following service extension is defined:
1. The name of the SMTP service extension is "Email Address
Internationalization".
2. The EHLO keyword value associated with this extension is
"UTF8SMTPbis".
3. No parameter values are defined for this EHLO keyword value. In
order to permit future (although unanticipated) extensions, the
EHLO response MUST NOT contain any parameters for that keyword.
Clients MUST ignore any parameters; that is, clients MUST behave
as if the parameters do not appear. If a server includes
UTF8SMTPbis in its EHLO response, it MUST be fully compliant with
this version of this specification.
4. One optional parameter "UTF8REPLY" is added to the VRFY and EXPN
commands. The parameter UTF8REPLY has no value. The parameter
indicates that the SMTP client can accept Unicode characters in
UTF-8 encoding in replies from the VRFY and EXPN commands.
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5. No additional SMTP verbs are defined by this extension.
6. Servers offering this extension MUST provide support for, and
announce, the 8BITMIME extension [RFC1652].
7. The reverse-path and forward-path of the SMTP MAIL and RCPT
commands are extended to allow Unicode characters encoded in
UTF-8 in mailbox names (addresses).
8. The mail message body is extended as specified in [RFC5335bis].
9. The UTF8SMTPbis extension is valid on the submission port
[RFC4409].
3.2. The UTF8SMTPbis Extension
An SMTP server that announces this extension MUST be prepared to
accept a UTF-8 string [RFC3629] in any position in which RFC 5321
specifies that a mailbox can appear. That string MUST be parsed only
as specified in RFC 5321, i.e., by separating the mailbox into source
route, local part, and domain part, using only the characters colon
(U+003A), comma (U+002C), and at-sign (U+0040) as specified there.
Once isolated by this parsing process, the local part MUST be treated
as opaque unless the SMTP server is the final delivery Mail Transfer
Agent (MTA). Any domain names to be looked up in the DNS MUST allow
for [RFC5890] behavior. When doing lookups, the server MUST either
use a Unicode aware DNS library, or transform it to A-label defined
in [RFC5890]. Any domain names that are to be compared to local
strings SHOULD be checked for validity and then MUST be compared as
specified in section 3 of [RFC5891].
An SMTP client that receives the UTF8SMTPbis extension keyword in
response to the EHLO command MAY transmit mailbox names within SMTP
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). It MAY transmit the domain parts of mailbox names within
SMTP commands or the message header as either ACE (ASCII Compatible
Encoding) labels (as specified in IDNA [RFC5890]) or UTF-8 strings.
All labels in 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 a Message Submission Server ("MSA") [RFC4409], it is the
responsibility of the MSA that all domain labels are valid;
otherwise, it is the original client's responsibility. The presence
of the UTF8SMTPbis extension does not change the requirement of RFC
5321 that servers relaying mail MUST NOT attempt to parse, evaluate,
or transform the local part in any way.
If the UTF8SMTPbis SMTP extension is not offered by the Server, the
SMTP client MUST NOT transmit an internationalized address and MUST
NOT transmit a mail message containing internationalized mail headers
as described in [RFC5335bis] at any level within its MIME structure.
(For this paragraph, the internationalized domain name in the form of
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ACE labels as specified in IDNA [RFC5890] is not considered as
"internationalized".) Instead, if an SMTP client (SMTP sender)
attempts to transfer an internationalized message and encounters a
server that does not support the extension, it MUST make one of the
following three choices:
1. If and only if the SMTP client (sender) is a Message Submission
Server ("MSA") [RFC4409], it MAY, consistent with the general
provisions for changes by such servers, rewrite the envelope,
headers, or message material to make them entirely ASCII and
consistent with the provisions of RFC 5321 [RFC5321] and RFC 5322
[RFC5322].
2. It may either reject the message during the SMTP transaction or
accept the message and then generate and transmit a notification
of non-deliverability. Such notification MUST be done as
specified in RFC 5321 [RFC5321], RFC 3464 [RFC3464], and the EAI
delivery status notification (DSN) specification [RFC5337bis].
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 SMTP-sender.
If a server advertises UTF8SMTP and the client does not recognize the
extension, the client may send a regular message [RFC5321] and
[RFC5322]. In this case, the client may continue to use the
[RFC5890] to transform the domain portion of an address to A-label
[RFC5890]. If the email address is in the format of ASCII@non-ASCII,
the legacy SMTP servers MUST reject the message with the
ASCII@non-ASCII if the non-ASCII domain part is not transformed into
the format of A-label by the client. UTF8SMTPbis servers MUST
recognize and decode the ACE label(s) as appropriate.
3.3. Extended Mailbox Address Syntax
RFC 5321, Section 4.1.2, defines the syntax of a mailbox entirely in
terms of ASCII characters, using the production for a mailbox and
those productions on which it depends.
The key changes made by this specification are, informally, to
o Change the definition of "sub-domain" to permit either the
definition above or a UTF-8 string representing a DNS label that
is conformant with IDNA [RFC5890].
o Change the definition of "Atom" to permit either the definition
above or a UTF-8 string. That string MUST NOT contain any of the
ASCII characters (either graphics or controls) that are not
permitted in "atext"; it is otherwise unrestricted.
According to the description above, the syntax of an
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internationalized email mailbox name (address) is defined in ABNF
[RFC5234] as follows.
uMailbox = uLocal-part "@" uDomain
; uLocal-part and uDomain defined
; in RFC 5335bis, Section 4.
The value of "uDomain" SHOULD be verified by IDNA [RFC5890]. If that
verification fails, the email address with that uDomain MUST NOT be
regarded as a valid email address.
3.4. UTF8 addresses and Response Codes
An "internationalized message" as defined in the appendix of this
specification MUST NOT be sent to an SMTP server that does not
support UTF8SMTPbis. Such a message should be rejected by a server
if it lacks the support of UTF8SMTPbis.
The three-digit reply codes used in this section are consistent with
their meanings as defined in RFC 5321.
When messages are rejected because the RCPT command requires an ASCII
address, the response code 553 is used with the meaning "mailbox name
not allowed". When messages are rejected for other reasons, such as
the MAIL command requiring an ASCII address, the response code 550 is
used with the meaning "mailbox unavailable". When the server
supports enhanced mail system status codes [RFC3463], response code
"X.6.7" [RFC5248] is used, meaning that "UTF-8 addresses not
permitted for that sender/recipient".
If the response code is issued after the final "." of the DATA
command, the response code "554" is used with the meaning
"Transaction failed". When the server supports enhanced mail system
status codes [RFC3463], response code "X.6.9" [RFC5248] is used,
meaning that "UTF-8 header message can't be transferred to one or
more recipient so the message must be bounced".
3.5. Body Parts and SMTP Extensions
There is no ESMTP parameter to assert that a message is an
internationalized message. An SMTP server that requires accurate
knowledge of whether a message is internationalized is required to
parse all message header fields and MIME header fields in the message
body.
While this specification requires that servers support the 8BITMIME
extension [RFC1652] to ensure that servers have adequate handling
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capability for 8-bit data and to avoid a number of complex encoding
problems, the use of internationalized addresses obviously does not
require non-ASCII body parts in the MIME message. The UTF8SMTPbis
extension MAY be used with the BODY=8BITMIME parameter if that is
appropriate given the body content or, with the BODY=BINARYMIME
parameter, if the server advertises BINARYMIME [RFC3030] and that is
appropriate.
Assuming that the server advertises UTF8SMTPbis and 8BITMIME, and
receives at least one non-ASCII address, the precise interpretation
of 'No BODY parameter', "BODY=8BITMIME", and "BODY=BINARYMIME" in the
MAIL command is:
1. If there is no BODY parameter, the header contains UTF-8
characters, but all the body parts are in ASCII (possibly as the
result of a content-transfer-encoding).
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
line-oriented data.
3. If a BODY=BINARYMIME parameter is present, the header contains
UTF-8 characters, and some or all body parts contain binary data
without restriction as to line lengths or delimiters.
3.6. Additional ESMTP Changes and Clarifications
The information carried in the mail transport process involves
addresses ("mailboxes") and domain names in various contexts in
addition to the MAIL and RCPT commands and extended alternatives to
them. In general, the rule is that, when RFC 5321 specifies a
mailbox, this specification expects UTF-8 to be used for the entire
string; when RFC 5321 specifies a domain name, the name SHOULD be in
the form of ACE labels if its raw form is non-ASCII.
The following subsections list and discuss all of the relevant cases.
3.6.1. The Initial SMTP Exchange
When an SMTP connection is opened, the server normally sends a
"greeting" response consisting of the 220 response code and some
information. The client then sends the EHLO command. Since the
client cannot know whether the server supports UTF8SMTPbis until
after it receives the response from EHLO, any domain names that
appear in this dialogue, or in responses to EHLO, MUST be in the
hostname form, i.e., internationalized ones MUST be in the form of
ACE labels.
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3.6.2. Mail eXchangers
Organizations often authorize multiple servers to accept mail
addressed to them. For example, the organization may itself operate
more than one server, and may also or instead have an agreement with
other organizations to accept mail as a backup. Authorized servers
are generally listed in MX records as described in RFC 5321. When
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
UTF8SMTPbis extension. Otherwise, surprising downgrades can happen
during temporary failures, which users might perceive as a serious
reliability issue.
3.6.3. Trace Information
When an SMTP server receives a message for delivery or further
processing, it MUST insert trace ("time stamp" or "Received")
information at the beginning of the message content. "Time stamp" or
"Received" appears in the form of "Received:" lines. The most
important use of Received: lines is for debugging mail faults. When
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
primary purpose of the Return-path is to designate the address to
which messages indicating non-delivery or other mail system failures
are to be sent. For the trace information, this memo updates the
time stamp line and the return path line [RFC5321] formally defined
as follows:
uReturn-path-line = "Return-Path:" FWS uReverse-path <CRLF>
; Replaces Return-path-line in Section 4.4 of RFC 5321
; uReverse-path is defined in Section 4 of RFC5335bis
uTime-stamp-line = "Received:" FWS uStamp <CRLF>
; Replaces Time-stamp-line in Section 4.4 of RFC 5321
uStamp = From-domain By-domain uOpt-info ";" FWS date-time
; Replaces Stamp in Section 4.4 of RFC 5321
uOpt-info = [Via] [With] [ID] [uFor]
; Replaces Opt-info in Section 4.4 of RFC 5321
; The protocol value for With will allow a UTF8SMTPbis value
uFor = "FOR" ( FWS (uPath / uMailbox) ) CFWS
; Replaces For in Section 4.4 of RFC 5321
; uMailbox is defined in section 3.3 of this document
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uPath = "<" [ A-d-l ":" ] uMailbox ">"
; Replace Path in RFC 5321, section 4.1.2
; A-d-l is defined in RFC 5321, section 4.1.2
; uMailbox is defined in section 3.3 of this document
Except in the 'uFor' clause and 'uReverse-path' value where non-ASCII
domain names may be used, internationalized domain names in Received
fields MUST be transmitted in the form of ACE labels. The protocol
value of the WITH clause when this extension is used is one of the
UTF8SMTPbis values specified in the "IANA Considerations" section of
this document.
3.6.4. UTF-8 Strings in Replies
3.6.4.1. MAIL and RCPT Commands
If the client issues a RCPT command containing non-ASCII characters,
the SMTP server is permitted to use UTF-8 characters in the email
address associated with 251 and 551 response codes.
If an SMTP client follows this specification and sends any RCPT
commands containing non-ASCII addresses, it MUST be able to accept
and process 251 or 551 responses containing UTF-8 email addresses.
If 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-ASCII mailbox. Instead, it MUST transform such responses into
250 or 550 responses that do not contain addresses.
3.6.4.2. VRFY and EXPN Commands and the UTF8REPLY Parameter
If the VRFY and EXPN commands are transmitted with the optional
parameter "UTF8REPLY", it indicates the client can accept UTF-8
strings in replies to those commands. This allows the server to use
UTF-8 strings in mailbox names and full names that occur in replies
without concern that the client might be confused by them. An SMTP
client that conforms to this specification MUST accept and correctly
process replies from the VRFY and EXPN commands that contain UTF-8
strings. However, the SMTP server MUST NOT use UTF-8 strings in
replies if the SMTP client does not specifically allow such replies
by transmitting this parameter. Most replies do not require that a
mailbox name be included in the returned text, and therefore UTF-8 is
not needed in them. Some replies, notably those resulting from
successful execution of the VRFY and EXPN commands, do include the
mailbox, making the provisions of this section important.
VERIFY (VRFY) and EXPAND (EXPN) command syntaxes are changed to:
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"VRFY" SP ( uLocal-part / uMailbox ) [ SP "UTF8REPLY" ] CRLF
; uLocal-part and uMailbox are defined in
; Section 3.3 of this document.
"EXPN" SP ( uLocal-part / uMailbox ) [ SP "UTF8REPLY" ] CRLF
; uLocal-part and uMailbox are defined in
; Section 3.3 of this document.
The "UTF8REPLY" parameter does not use a value. If the reply to a
VERIFY (VRFY) or EXPAND (EXPN) command requires UTF-8, but the SMTP
client did not use the "UTF8REPLY" parameter, then the server MUST
use either the response code 252 or 550. Response code 252, defined
in [RFC5321], means "Cannot VRFY user, but will accept the message
and attempt the delivery". Response code 550, also defined in
[RFC5321], means "Requested action not taken: mailbox unavailable".
When the server supports enhanced mail system status codes [RFC3463],
the enhanced response code as specified below is used. Using the
"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
MAY include the full name of the user and MUST include the mailbox of
the user. It MUST be in either of the following forms:
User Name <uMailbox>
; uMailbox is defined in Section 3.3 of this document.
; User Name can contain non-ASCII characters.
uMailbox
; uMailbox is defined in Section 3.3 of this document.
If the SMTP reply requires UTF-8 strings, but UTF-8 is not allowed in
the reply, and the server supports enhanced mail system status codes
[RFC3463], the enhanced response code is either "X.6.8" or "X.6.10"
[RFC5248], meaning "A reply containing a UTF-8 string is required to
show the mailbox name, but that form of response is not permitted by
the client".
If the SMTP client does not support the UTF8SMTPbis extension, but
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 crash.
Internationalized messages in replies are only allowed in the
commands under the situations described above. Under any other
circumstances, UTF-8 text MUST NOT appear in the reply.
Although UTF-8 is needed to represent email addresses in responses
under the rules specified in this section, this extension does not
permit the use of UTF-8 for any other purposes. SMTP servers MUST
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NOT include non-ASCII characters in replies except in the limited
cases specifically permitted in this section.
4. IANA Considerations
IANA has added a new value "UTF8SMTPbis" to the SMTP Service
Extension subregistry of the Mail Parameters registry, according to
the following data:
+-------------+---------------------------------+-----------+
| Keywords | Description | Reference |
+-------------+---------------------------------+-----------+
| UTF8SMTPbis | Internationalized email address | [RFCXXXX] |
+-------------+---------------------------------+-----------+
This document updates the values to the SMTP Enhanced Status Code
subregistry of the Mail Parameters registry, following the guidance
in Sections 3.4 and 3.6.4.2 of this document, and being based on
[RFC5248]. The registration data is as follows:
Code: X.6.7
Sample Text: UTF-8 addresses not permitted
for that sender/recipient
Associated basic status code: 553, 550
Description: This indicates the reception of a MAIL or RCPT
command that rUTF-8 addresses are not permitted
Defined: RFC XXXX (Standard track)
Submitter: Jiankang YAO
Change controller: IESG.
Code: X.6.8
Sample Text: UTF-8 string reply is required,
but not permitted by the client
Associated basic status code: 553, 550
Description: This indicates that a reply containing a UTF-8
string is required to show the mailbox name,
but that form of response is not
permitted by the client.
Defined: RFC XXXX (Standard track)
Submitter: Jiankang YAO
Change controller: IESG.
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Code: X.6.9
Sample Text: UTF-8 header message can't be transferred
to one or more recipient so the message
must be bounced
Associated basic status code: 550
Description: This indicates that transaction failed
after the final "." of the DATA command.
Defined: RFC XXXX (Standard track)
Submitter: Jiankang YAO
Change controller: IESG.
Code: X.6.10
Sample Text: UTF-8 string reply is required,
but not permitted by the client
Associated basic status code: 252
Description: This indicates that a reply containing a UTF-8
string is required to show the mailbox name,
but that form of response is not
permitted by the client.
Defined: RFC XXXX (Standard track)
Submitter: Jiankang YAO
Change controller: IESG.
The "Mail Transmission Types" registry under the Mail Parameters
registry is requested to be updated to include the following new
entries:
+---------------+-----------------------------+---------------------+
| WITH protocol | Description | Reference |
| types | | |
+---------------+-----------------------------+---------------------+
| UTF8SMTPbis | UTF8SMTPbis with Service | [RFCXXXX] |
| | Extensions | |
| UTF8SMTPbisA | UTF8SMTPbis with SMTP AUTH | [RFC4954] [RFCXXXX] |
| UTF8SMTPbisS | UTF8SMTPbis with STARTTLS | [RFC3207] [RFCXXXX] |
| UTF8SMTPbisSA | UTF8SMTPbis with both | [RFC3207] [RFC4954] |
| | STARTTLS and SMTP AUTH | [RFCXXXX] |
+---------------+-----------------------------+---------------------+
5. Security Considerations
See the extended security considerations discussion in the framework
document [RFC4952bis].
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6. Acknowledgements
Much of the text in the initial version of this specification was
derived or copied from [Emailaddr] with the permission of the author.
Significant comments and suggestions were received from Xiaodong LEE,
Nai-Wen Hsu, Yangwoo KO, Yoshiro YONEYA, and other members of the JET
team and were incorporated into the specification. Additional
important comments and suggestions, and often specific text, were
contributed by many members of the WG and design team. Those
contributions include material from John C Klensin, Charles Lindsey,
Dave Crocker, Harald Tveit Alvestrand, Marcos Sanz, Chris Newman,
Martin Duerst, Edmon Chung, Tony Finch, Kari Hurtta, Randall Gellens,
Frank Ellermann, Alexey Melnikov, Pete Resnick, S. Moonesamy, Soobok
Lee, Shawn Steele, Alfred Hoenes, Miguel Garcia, Magnus Westerlund,
and Lars Eggert. Of course, none of the individuals are necessarily
responsible for the combination of ideas represented here.
7. Change History
[[anchor11: 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.
8. References
8.1. Normative References
[ASCII] American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, 1968.
[RFC1652] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
RFC 1652, July 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Internet-Draft EAI SMTP Extension August 2010
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)",
RFC 3461, January 2003.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, January 2003.
[RFC3464] Moore, K. and G. Vaudreuil, "An Extensible Message Format
for Delivery Status Notifications", RFC 3464,
January 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, November 2003.
[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", RFC 4952, July 2007.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5248] Hansen , T. and J. Klensin, "A Registry for SMTP Enhanced
Mail System Status Codes", RFC 5248, June 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[RFC5335bis]
Abel, Y., Ed., "Internationalized Email Headers",
RFC 5335, August 2008.
[RFC5337bis]
Newman, C. and A. Melnikov, Ed., "Internationalized
Delivery Status and Disposition Notifications", RFC 5337,
August 2008.
[RFC5890] Klensin, J., "Internationalizing Domain Names in
Applications (IDNA)", RFC 5890, June 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in
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Internet-Draft EAI SMTP Extension August 2010
Applications (IDNA): Protocol", RFC 5891, August 2010.
8.2. Informative References
[Emailaddr]
Klensin, J., "Internationalization of Email Addresses",
draft-klensin-emailaddr-i18n-03 (work in progress),
July 2005.
[RFC0974] Partridge, C., "Mail routing and the domain system",
RFC 974, January 1986.
[RFC2033] Myers, J., "Local Mail Transfer Protocol", RFC 2033,
October 1996.
[RFC3030] Vaudreuil, G., "SMTP Service Extensions for Transmission
of Large and Binary MIME Messages", RFC 3030,
December 2000.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension
for Authentication", RFC 4954, July 2007.
Appendix A. Additional Material
A.1. Conventional Message and Internationalized Message
o A conventional message is one that does not use any extension
defined in this document or in the UTF-8 header specification
[RFC5335bis], and which is strictly conformant to RFC 5322
[RFC5322].
o An internationalized message is a message utilizing one or more of
the extensions defined in this specification or in the UTF-8
header specification [RFC5335bis], so that it is no longer
conformant to the RFC 5322 specification of a message.
A.2. LMTP
LMTP [RFC2033] may be used as the final delivery agent. In such
cases, LMTP may be arranged to deliver the mail to the mail store.
The mail store may not have UTF8SMTPbis capability. LMTP needs to be
updated to deal with these situations.
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A.3. SMTP Service Extension for DSNs
The existing Draft Standard regarding delivery status notifications
(DSNs) [RFC3461] is limited to ASCII text in the machine readable
portions of the protocol. "International Delivery and Disposition
Notifications" [RFC5337bis] adds a new address type for international
email addresses so an original recipient address with non-ASCII
characters can be correctly preserved even after downgrading. If an
SMTP server advertises both the UTF8SMTPbis and the DSN extension,
that server MUST implement EAI DSN [RFC5337bis] including support for
the ORCPT parameter.
A.4. Implementation Advice
In the absence of this extension, SMTP clients and servers are
constrained to using only those addresses permitted by RFC 5321. The
local parts of those addresses MAY be made up of any ASCII
characters, although some of them MUST be quoted as specified there.
It is notable in an internationalization context that there is a long
history on some systems of using overstruck ASCII characters (a
character, a backspace, and another character) within a quoted string
to approximate non-ASCII characters. This form of
internationalization SHOULD be phased out as this extension becomes
widely deployed, but backward-compatibility considerations require
that it continue to be supported.
Authors' Addresses
Jiankang YAO (editor)
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing
Phone: +86 10 58813007
Email: yaojk@cnnic.cn
Wei MAO (editor)
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing
Phone: +86 10 58812230
Email: maowei_ietf@cnnic.cn
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