Network Working Group J. Yao, Ed. Internet-Draft W. Mao, Ed. Obsoletes: RFC5336 CNNIC (if approved) June 24, 2010 Updates: RFC2821 and 2822 (if approved) Intended status: Standards Track Expires: December 26, 2010 SMTP Extension for Internationalized Email Address draft-ietf-eai-rfc5336bis-00.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 2821 and RFC 2822. 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 December 26, 2010. 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 Yao & Mao Expires December 26, 2010 [Page 1]
Internet-Draft EAI SMTP Extension June 2010 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 10, 2008. The person(s) controlling the copyright in some of this 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. Yao & Mao Expires December 26, 2010 [Page 2]
Internet-Draft EAI SMTP Extension June 2010 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 . . . . . . . . . . . . 9 3.5. Body Parts and SMTP Extensions . . . . . . . . . . . . . . 9 3.6. Additional ESMTP Changes and Clarifications . . . . . . . 10 3.6.1. The Initial SMTP Exchange . . . . . . . . . . . . . . 10 3.6.2. Mail eXchangers . . . . . . . . . . . . . . . . . . . 10 3.6.3. Trace Information . . . . . . . . . . . . . . . . . . 11 3.6.4. UTF-8 Strings in Replies . . . . . . . . . . . . . . . 12 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 7. Change History . . . . . . . . . . . . . . . . . . . . . . . . 16 7.1. draft-yao-eai-rfc5336bis: Version 00 . . . . . . . . . . . 16 7.2. draft-ietf-eai-rfc5336bis: Version 00 . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . . 16 8.2. Informative References . . . . . . . . . . . . . . . . . . 17 Appendix A. Additional Material . . . . . . . . . . . . . . . . . 18 A.1. Conventional Message and Internationalized Message . . . . 18 A.2. LMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 A.3. SMTP Service Extension for DSNs . . . . . . . . . . . . . 18 A.4. Implementation Advice . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Yao & Mao Expires December 26, 2010 [Page 3]
Internet-Draft EAI SMTP Extension June 2010 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 [RFC2821] 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 [RFC2821] [RFC2822] 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 [RFC2821] 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 [RFC2821] [RFC2822]. 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. Yao & Mao Expires December 26, 2010 [Page 4]
Internet-Draft EAI SMTP Extension June 2010 This specification defines only those Augmented BNF (ABNF) [RFC5234] syntax rules that are different from those of the base email specifications [RFC2821][RFC2822] and, where the earlier rules are upgraded or extended, gives them new names. When the new rule is a small 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. Yao & Mao Expires December 26, 2010 [Page 5]
Internet-Draft EAI SMTP Extension June 2010 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 2821 specifies that a mailbox can appear. That string MUST be parsed only as specified in RFC 2821, i.e., by separating the mailbox into source route, local part, and domain part, using only the characters colon (U+003A), comma (U+002C), and at-sign (U+0040) as specified there. Once isolated by this parsing process, the local part MUST be treated as opaque unless the SMTP server is the final delivery 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 do ToAscii() defined in [RFC3490] or [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 [RFC3490] and [RFC5890]. 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 [RFC3490]) 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 2821 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 Yao & Mao Expires December 26, 2010 [Page 6]
Internet-Draft EAI SMTP Extension June 2010 ACE labels as specified in IDNA [RFC3490] and [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 2821 [RFC2821] and RFC 2822 [RFC2822]. 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 2821 [RFC2821], 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 2821) 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 [RFC2821] and [RFC2822]. In this case, the client may continue to use the [RFC3490] or [RFC5890] ToAscii() to encode the domain portion of an address. UTF8SMTP servers MUST recognize and decode the ACE label(s) as appropriate. 3.3. Extended Mailbox Address Syntax RFC 2821, Section 4.1.2, defines the syntax of a mailbox entirely in terms of ASCII characters, using the production for 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 [RFC3490]. 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 internationalized email mailbox name (address) is defined in ABNF [RFC5234] as follows. Yao & Mao Expires December 26, 2010 [Page 7]
Internet-Draft EAI SMTP Extension June 2010 uMailbox = uLocal-part "@" uDomain ; Replace Mailbox in RFC 2821, Section 4.1.2 uLocal-part = uDot-string / uQuoted-string ; MAY be case-sensitive ; Replace Local-part in RFC 2821, Section 4.1.2 uDot-string = uAtom *("." uAtom) ; Replace Dot-string in RFC 2821, Section 4.1.2 uAtom = 1*ucharacter ; Replace Atom in RFC 2821, Section 4.1.2 ucharacter = atext / UTF8-non-ascii atext = <See Section 3.2.4 of RFC 2822> uQuoted-string = DQUOTE *uqcontent DQUOTE ; Replace Quoted-string in RFC 2821, Section 4.1.2 DQUOTE = <See appendix B.1 of RFC 5234> uqcontent = qcontent / UTF8-non-ascii qcontent = <See Section 3.2.5 of RFC 2822> uDomain = (sub-udomain 1*("." sub-udomain)) / address-literal ; Replace Domain in RFC 2821, Section 4.1.2 address-literal = <See Section 4.1.2 of RFC 2822> sub-udomain = uLet-dig [uLdh-str] ; Replace sub-domain in RFC 2821, Section 4.1.2 uLet-dig = Let-dig / UTF8-non-ascii Let-dig = <See Section 4.1.3 of RFC 2821> uLdh-str = *( ALPHA / DIGIT / "-" / UTF8-non-ascii) uLet-dig ; Replace Ldh-str in RFC 2821, Section 4.1.3 UTF8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4 UTF8-2 = <See Section 4 of RFC 3629> UTF8-3 = <See Section 4 of RFC 3629> UTF8-4 = <See Section 4 of RFC 3629> Yao & Mao Expires December 26, 2010 [Page 8]
Internet-Draft EAI SMTP Extension June 2010 The value of "uDomain" SHOULD be verified by applying the tests specified as part of IDNA [RFC3490]. 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 2821. 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 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. Yao & Mao Expires December 26, 2010 [Page 9]
Internet-Draft EAI SMTP Extension June 2010 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 2821 specifies a mailbox, this specification expects UTF-8 to be used for the entire string; when RFC 2821 specifies a domain name, the name SHOULD be in the form of ACE labels if its raw form is non-ASCII. 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. 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 2821. 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 Yao & Mao Expires December 26, 2010 [Page 10]
Internet-Draft EAI SMTP Extension June 2010 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 [RFC2821] formally defined as follows: uReturn-path-line = "Return-Path:" FWS uReverse-path <CRLF> ; Replaces Return-path-line in Section 4.4 of RFC 2821 ; uReverse-path is defined in Section 3.3 of this document uTime-stamp-line = "Received:" FWS uStamp <CRLF> ; Replaces Time-stamp-line in Section 4.4 of RFC 2821 uStamp = From-domain By-domain uOpt-info ";" FWS date-time ; Replaces Stamp in Section 4.4 of RFC 2821 uOpt-info = [Via] [With] [ID] [uFor] ; Replaces Opt-info in Section 4.4 of RFC 2821 ; The protocol value for With will allow a UTF8SMTPbis value uFor = "FOR" ( FWS (uPath / uMailbox) ) CFWS ; Replaces For in Section 4.4 of RFC 2821 ; uPath and uMailbox are defined in Sections 3.4 and ; 3.3, respectively, of this document Note: The FOR parameter has been changed to match the definition in [RFC5321], permitting only one address in the For clause. The group working on that document reached mailing list consensus that the syntax in [RFC2821] that permitted more than one address was simply a mistake. 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. Yao & Mao Expires December 26, 2010 [Page 11]
Internet-Draft EAI SMTP Extension June 2010 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: "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 [RFC2821], means "Cannot VRFY user, but will accept the message Yao & Mao Expires December 26, 2010 [Page 12]
Internet-Draft EAI SMTP Extension June 2010 and attempt the delivery". Response code 550, also defined in [RFC2821], 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 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: Yao & Mao Expires December 26, 2010 [Page 13]
Internet-Draft EAI SMTP Extension June 2010 +-------------+---------------------------------+-----------+ | 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. 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. Yao & Mao Expires December 26, 2010 [Page 14]
Internet-Draft EAI SMTP Extension June 2010 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]. 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 Yao & Mao Expires December 26, 2010 [Page 15]
Internet-Draft EAI SMTP Extension June 2010 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. 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 Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)", RFC 3461, January 2003. [RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 3463, January 2003. [RFC3464] Moore, K. and G. Vaudreuil, "An Extensible Message Format for Delivery Status Notifications", RFC 3464, Yao & Mao Expires December 26, 2010 [Page 16]
Internet-Draft EAI SMTP Extension June 2010 January 2003. [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 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. [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. 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, Yao & Mao Expires December 26, 2010 [Page 17]
Internet-Draft EAI SMTP Extension June 2010 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 2822 [RFC2822]. 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 2822 specification of a message. A.2. LMTP LMTP [RFC2033] may be used as the final delivery agent. In such cases, LMTP may be arranged to deliver the mail to the mail store. The mail store may not have UTF8SMTPbis capability. LMTP needs to be updated to deal with these situations. 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. Yao & Mao Expires December 26, 2010 [Page 18]
Internet-Draft EAI SMTP Extension June 2010 A.4. Implementation Advice In the absence of this extension, SMTP clients and servers are constrained to using only those addresses permitted by RFC 2821. The local parts of those addresses MAY be made up of any ASCII characters, although some of them MUST be quoted as specified there. It is notable in an internationalization context that there is a long history on some systems of using overstruck ASCII characters (a character, a backspace, and another character) within a quoted string to approximate non-ASCII characters. This form of internationalization SHOULD be phased out as this extension becomes widely deployed, but backward-compatibility considerations require that it continue to be supported. 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 Yao & Mao Expires December 26, 2010 [Page 19]
