From: http://www.ietf.org/internet-drafts/draft-ietf-eai-utf8headers-12.txt Title: Internationalized Email Headers Reference: IETF Network Working Group, Internet Draft 'draft-ietf-eai-utf8headers-12.txt' Date: July 09, 2008 I-D Tracker: http://ietfreport.isoc.org/idref/draft-ietf-eai-utf8headers/ Tools: http://tools.ietf.org/html/draft-ietf-eai-utf8headers-12 See also: SMTP Extension for Internationalized Email Address http://xml.coverpages.org/draft-ietf-eai-smtpext-13.txt IETF Email Address Internationalization (EAI) Working Group Charter http://www.ietf.org/html.charters/eai-charter.html Overview and Framework for Internationalized Email http://www.ietf.org/rfc/rfc4952.txt IETF Email Address Internationalization WG Status Pages http://tools.ietf.org/wg/eai/ IETF Applications Area http://www.apps.ietf.org/ ============================================================================== Network Working Group Y. Abel, Ed. Internet-Draft TWNIC Intended status: Experimental July 09, 2008 Expires: January 10, 2009 Internationalized Email Headers draft-ietf-eai-utf8headers-12.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 10, 2009. Abstract Full internationalization of electronic mail requires not only the capability to transmit non-ASCII content, to encode selected information in specific header fields, and to use non-ASCII characters in envelope addresses. It also requires being able to express those addresses and information based on them in mail header fields. This document specifies an experimental variant of Internet mail that permits the use of Unicode encoded in UTF-8, rather than ASCII, as the base form for Internet email header field bodies. This form is permitted in transmission only if authorized by an SMTP extension, as specified in an associated specification. And this specification updates section 6.4 of [RFC2045] to conform with the requirements. Abel Expires January 10, 2009 [Page 1] Internet-Draft I18N Email Headers July 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Role of this specification . . . . . . . . . . . . . . . . 3 1.2. Relation to other standards . . . . . . . . . . . . . . . 3 2. Background and History . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Changes on Message Header Fields . . . . . . . . . . . . . . . 5 4.1. UTF8 Syntax and Normalization . . . . . . . . . . . . . . 5 4.2. Changes on MIME headers . . . . . . . . . . . . . . . . . 6 4.3. Syntax extensions to RFC 2822 . . . . . . . . . . . . . . 6 4.4. Change on addr-spec syntax . . . . . . . . . . . . . . . . 8 4.5. Trace field syntax . . . . . . . . . . . . . . . . . . . . 9 4.6. message/global . . . . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 8. Edit history . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. draft-ietf-eai-utf8header-12 . . . . . . . . . . . . . . . 12 8.2. draft-ietf-eai-utf8header-11 . . . . . . . . . . . . . . . 12 8.3. draft-ietf-eai-utf8header-10 . . . . . . . . . . . . . . . 12 8.4. draft-ietf-eai-utf8header-09 . . . . . . . . . . . . . . . 13 8.5. draft-ietf-eai-utf8header-08 . . . . . . . . . . . . . . . 13 8.6. draft-ietf-eai-utf8header-07 . . . . . . . . . . . . . . . 13 8.7. draft-ietf-eai-utf8header-06 . . . . . . . . . . . . . . . 13 8.8. draft-ietf-eai-utf8header-05 . . . . . . . . . . . . . . . 13 8.9. draft-ietf-eai-utf8header-04 . . . . . . . . . . . . . . . 13 8.10. draft-ietf-eai-utf8header-03 . . . . . . . . . . . . . . . 13 8.11. draft-ietf-eai-utf8header-02 . . . . . . . . . . . . . . . 14 8.12. draft-ietf-eai-utf8header-01 . . . . . . . . . . . . . . . 14 8.13. draft-ietf-eai-utf8header-00 . . . . . . . . . . . . . . . 14 8.14. draft-yeh-ima-utf8header-01 . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . . 14 9.2. Informative References . . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 17 Abel Expires January 10, 2009 [Page 2] Internet-Draft I18N Email Headers July 2008 1. Introduction 1.1. Role of this specification Full internationalization of electronic mail requires several capabilities: o The capability to transmit non-ASCII content, provided for as part of the basic MIME specification [RFC2045], [RFC2046]. o The capability to use international characters in envelope addresses, discussed in [RFC4952] and specified in [I-D.ietf-eai-smtpext]. o The capability to express those addresses, and information related to them and based on them, in mail header fields, defined in this document. This document specifies an experimental variant of Internet mail that permits the use of Unicode encoded in UTF-8 [RFC3629], rather than ASCII, as the base form for Internet email header fields. This form is permitted in transmission, if authorized by the SMTP extension specified in [I-D.ietf-eai-smtpext] or by other transport mechanisms capable of processing it. 1.2. Relation to other standards This document updates section 6.4 of RFC 2045. It removes the blanket ban on applying a content-transfer-encoding to all subtypes of message/, and instead specifies that a composite subtype MAY specify whether or not a content-transfer-encoding can be used for that subtype, with "cannot be used" as the default. This document also updates [RFC2822] and MIME ([RFC2045]), and the fact that an experimental specification updates a standards-track spec means that people who participate in the experiment have to consider those standards updated. Allowing of use a content-transfer-encoding on subtypes of messages is not limited to transmissions, which are authorized by the SMTP extension specified in [I-D.ietf-eai-smtpext]. Message/global permits use of a content-transfer-encoding. 2. Background and History Mailbox names often represent the names of human users. Many of these users throughout the world have names that are not normally expressed with just the ASCII repertoire of characters, and would like to use more or less their real names in their mailbox names. Abel Expires January 10, 2009 [Page 3] Internet-Draft I18N Email Headers July 2008 These users are also likely to use non-ASCII text in their common names and subjects of email messages, both in what they send and what they receive. This protocol specifies UTF-8 as the encoding to represent email header field bodies. The traditional format of email messages [RFC2822] allows only ASCII characters in the header fields of messages. This prevents users from having email addresses that contain non-ASCII characters. It further forces non-ASCII text in common names, comments, and in free text (such as in the Subject: field) to be encoded (as required by MIME format [RFC2047]). This specification describes a change to the email message format that is related to the SMTP message transport change described in the associated document [RFC4952] and [I-D.ietf-eai-smtpext], and that allows non-ASCII characters in most email header fields. These changes affect SMTP clients, SMTP servers, mail user agents (MUAs), list expanders, gateways to other media, and all other processes that parse or handle email messages. As specified in [I-D.ietf-eai-smtpext], an SMTP protocol extension "UTF8SMTP" is used to prevent the transmission of messages with UTF-8 header fields to systems that cannot handle such messages. Use of this SMTP extension helps prevents the introduction of such messages into message stores that might misinterpret, improperly display, or mangle such messages. It should be noted that using an ESMTP extension does not prevent transfering email messages with UTF-8 header fields to other systems that use the email format for messages and that may not be upgraded, such as unextended POP and IMAP servers. Changes to these protocols to handle UTF-8 header fields are addressed in [I-D.ietf-eai-pop] and [I-D.ietf-eai-imap-utf8] . The objective for this protocol is to allow UTF-8 in email header fields. Issues such as how to handle messages containing UTF-8 header fields that have to be delivered to systems that have not been upgraded to support this capability are discussed in [I-D.ietf-eai-downgrade]. 3. Terminology A plain ASCII string is also a valid UTF-8 string, see [RFC3629]. In this document, ordinary ASCII characters are UTF-8 characters if they are in headers which contain s. Unless otherwise noted, all terms used here are defined in [RFC2821], [RFC2822], [RFC4952], or [I-D.ietf-eai-smtpext]. Abel Expires January 10, 2009 [Page 4] Internet-Draft I18N Email Headers July 2008 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 [RFC2119]. This document is discussed on the ima mailing list. See https://www1.ietf.org/mailman/listinfo/ima for information about subscribing. The list's archive is at http://www1.ietf.org/mail-archive/web/ima/index.html. 4. Changes on Message Header Fields SMTP clients can send header fields in UTF-8 format, if the UTF8SMTP extension is advertised by the SMTP server or as permitted by other transport mechanisms. This protocol does NOT change the [RFC2822] rules for defining header field names. The bodies of header fields are allowed to contain UTF-8 characters, but the header field names themselves must contain only ASCII characters. To permit UTF-8 characters in field values, the header definition in [RFC2822] must be extended to support new format. The following ABNF is defined to substitute those definition in [RFC2822]. The syntax rules not covered in this section remain as defined in [RFC2822]. 4.1. UTF8 Syntax and Normalization UTF-8 characters can be defined in terms of octets using the following ABNF, taken from [RFC3629]: UTF8-xtra-char = UTF8-2 / UTF8-3 / UTF8-4 UTF8-2 = %xC2-DF UTF8-tail UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2(UTF8-tail) / %xED %x80-9F UTF8-tail / %xEE-EF 2(UTF8-tail) UTF8-4 = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) / %xF4 %x80-8F 2( UTF8-tail ) UTF8-tail = %x80-BF Abel Expires January 10, 2009 [Page 5] Internet-Draft I18N Email Headers July 2008 These are normatively defined in [RFC3629], but kept in this document for reasons of convenience. See [RFC5198] for a discussion of normalization, the use of normalization form NFC is RECOMMENDED. 4.2. Changes on MIME headers This specification updates section 6.4 of [RFC2045]. [RFC2045] prohibits applying a content-transfer-encoding to all subtypes of message/. This specification relaxes the rule, allowing newly defined MIME types to permit content-transfer-encoding, and permits content-transfer-encoding for message/global (see Section 4.6). Background: Normally, transfer of message/global will be done in 8-bit-clean channels, and body parts will have "identity" encodings, that is, no decoding is necessary. In the case where a message containing a message/global is downgraded from 8-bit to 7-bit as described in [RFC1652]., an encoding may be applied to the message; if the message travels multiple times between a 7-bit environment and an environment implementing UTF8SMTP, multiple levels of encoding may occur. This is expected to be rarely seen in practice, and the potential complexity of other ways of dealing with the issue are thought to be larger than the complexity of allowing nested encodings where necessary. 4.3. Syntax extensions to RFC 2822 The following rules intended to extend the corresponding rules in [RFC2822] to allow UTF8 characters. FWS = CFWS = ctext =/ UTF8-xtra-char utext =/ UTF8-xtra-char comment = "(" *([FWS] utf8-ccontent) [FWS] ")" word = utf8-atom / utf8-quoted-string This means that all the [RFC2822] constructs that build upon these will permit UTF-8 characters, including comments and quoted strings. We do not change the syntax of in order to allow UTF8 Abel Expires January 10, 2009 [Page 6] Internet-Draft I18N Email Headers July 2008 characters in , because this would also allow UTF8 characters in , it is not allowed due to the limitation described in Section 4.5. Instead, is added to meet this requirement. utf8-text = %d1-9 / ; all UTF-8 characters except %d11-12 / ; US-ASCII NUL, CR and LF %d14-127 / UTF8-xtra-char utf8-quoted-pair = ("\" utf8-text) / obs-qp utf8-qcontent = utf8-qtext / utf8-quoted-pair utf8-quoted-string = [CFWS] DQUOTE *([FWS] utf8-qcontent) [FWS] DQUOTE [CFWS] utf8-ccontent = ctext / utf8-quoted-pair / comment utf8-qtext= qtext / UTF8-xtra-char utf8-atext = ALPHA / DIGIT / "!" / "#" / ; Any character except "$" / "%" / ; controls, SP, and specials. "&" / "'" / ; Used for atoms "*" / "+" / "-" / "/" / "=" / "?" / "^" / "_" / "`" / "{" / "|" / "}" / "~" / UTF8-xtra-char utf8-atom = [CFWS] 1*utf8-atext [CFWS] utf8-dot-atom = [CFWS] utf8-dot-atom-text [CFWS] utf8-dot-atom-text = 1*utf8-atext *("." 1*utf8-atext) qcontent = utf8-qcontent To allow the use of UTF-8 in a Content-Description header field [RFC2045], the following syntax is used: description = "Content-Description:" unstructured CRLF Abel Expires January 10, 2009 [Page 7] Internet-Draft I18N Email Headers July 2008 The syntax is extended above to allow UTF-8 in all header fields. Note, however, this does not remove any constraint on the character set of protocol elements; for instance, all the allowed values for timezone in the Date: headers are still expressed in ASCII. And also, none of this revised syntax changes what is allowed in a , which will still remain in pure ASCII. 4.4. Change on addr-spec syntax Internationalized email addresses are represented in UTF-8. Thus, all header fields containing es are updated to permit UTF-8 as well as an additional, optional all-ascii alternate address. Note that MSAs and MTAs may downgrade internationalized messages as needed. The procedure for doing so is described in [I-D.ietf-eai-downgrade]. mailbox = name-addr / addr-spec / utf8-addr-spec angle-addr =/ [CFWS] "<" utf8-addr-spec [ alt-address ] ">" [CFWS] / obs-angle-addr utf8-addr-spec = utf8-local-part "@" utf8-domain utf8-local-part= utf8-dot-atom / utf8-quoted-string / obs-local-part utf8-domain = utf8-dot-atom / domain-literal / obs-domain alt-address = FWS "<" addr-spec ">" Below list a few possible representation as example. "DISPLAY_NAME" ; traditional mailbox format "DISPLAY_NAME" ; UTF8SMTP but no ALT-ADDRESS parameter provided, ; message will bounce if UTF8SMTP extension is not supported ; without DISPLAY_NAME and quoted string ; UTF8SMTP but no ALT-ADDRESS parameter provided, ; message will bounce if UTF8SMTP extension is not supported "DISPLAY_NAME" > ; UTF8SMTP with ALT-ADDRESS parameter provided, ; ALT-ADDRESS can be used if downgrade is necessary Abel Expires January 10, 2009 [Page 8] Internet-Draft I18N Email Headers July 2008 4.5. Trace field syntax "For" fields containing internationalized addresses are allowed, by use of the new uFor syntax. UTF-8 information may be needed in Received fields. Such information is therefore allowed to preserve the integrity of those fields. The uFor syntax retains the original UTF-8 email address between EAI-aware MTAs. Note that, should downgrading be required, the uFor parameter is dropped per the procedure specified in [I-D.ietf-eai-downgrade]. The "Return-Path" header provides the email return address in the mail delivery. Thus, it is augmented to carry UTF8 addresses (see the revised syntax of in Section 4.4 of this document). This will not break the rule of trace field integrity, because it is added at the last MTA. The on "Received:" syntax is augmented to allow UTF-8 email address on "For" clause. is augmented to include UTF-8 email address. To allow UTF-8 email address also on syntax corresponding of on original syntax, is added to . item-value =/ utf8-addr-spec 4.6. message/global Internationalized messages must only be transmitted as authorized by [I-D.ietf-eai-smtpext] or within a non-SMTP environment which supports these messages. A message is a "message/global message", if o it contains UTF-8 header values as specified in this document, or o it contains UTF-8 values in the headers fields of body parts. The type message/global is similar to message/rfc822, except that it contains a message that can contain UTF-8 characters in the headers of the message or body parts. If this type is sent to a 7-bit-only system, it has to be encoded in [RFC2045]. (Note that a system compliant with MIME that doesn't recognize message/global would treat it as "application/octet-stream" as described in Section 5.2.4 of [RFC2046].) Alternatively, SMTP servers and other systems which transfer a message/global body part MAY choose to down-convert it to a message/ rfc822 body part using the rules described in [I-D.ietf-eai-downgrade]. Abel Expires January 10, 2009 [Page 9] Internet-Draft I18N Email Headers July 2008 Type name: message Subtype name: global Required parameters: none Optional parameters: none Encoding considerations: Any content-transfer-encoding is permitted. The 8-bit or binary content-transfer-encodings are recommended where permitted. Security considerations: See Section 5 Interoperability considerations: The media type provides functionality similar to the message/rfc822 content type for email messages with international email headers. When there is a need to embed or return such content in another message, there is generally an option to use this media type and leave the content unchanged or downconvert the content to message/rfc822. Both of these choices will interoperate with the installed base, but with different properties. Systems unaware of international headers will typically treat a message/global body part as an unknown attachment, while they will understand the structure of a message/ rfc822. However, systems which understand message/global will provide functionality superior to the result of a down-conversion to message/rfc822. The most interoperable choice depends on the deployed software. Published specification: RFC XXXX Applications that use this media type: SMTP servers and email clients that support multipart/report generation or parsing. Email clients which forward messages with international headers as attachments. Additional information: Magic number(s): none File extension(s): The extension ".u8msg" is suggested. Macintosh file type code(s): A uniform type identifier (UTI) of "public.utf8-email-message" is suggested. This conforms to "public.message" and "public.composite-content" but does not necessarily conform to "public.utf8-plain-text". Abel Expires January 10, 2009 [Page 10] Internet-Draft I18N Email Headers July 2008 Person & email address to contact for further information: See the Author's address section of this document. Intended usage: COMMON Restrictions on usage: This is a structured media type which embeds other MIME media types. The 8-bit or binary content-transfer- encoding MUST be used unless this media type is sent over a 7-bit only transport. Author: See Author's Address section of this document. Change controller: IETF Standards Process 5. Security Considerations If a user has a non-ASCII mailbox address and an ASCII mailbox address, a digital certificate that identifies that user may have both addresses in the identity. Having multiple email addresses as identities in a single certificate is already supported in PKIX and OpenPGP. Because UTF-8 often requires several octets to encode a single character, internationalized local parts may cause mail addresses to become longer. As specified in [RFC2822], each line of characters MUST be no more 998 octets, excluding the CRLF. Because internationalized local parts may cause email addresses to be longer, processes which parse, store, or handle email addresses or local parts must take extra care not to overflow buffers, truncate addresses, exceed storage allotments, or, when comparing, fail to use the entire length. In this specification, a user could provide an ASCII alternative address for a non-ASCII address. However, it is possible these two address go to different mailboxes, or even different persons. This configuration may be based on a user's personal choice, or based on administration policy. We recognize that if ASCII and non-ASCII email is delivered to two different destinations, based on MTA capability, this may violate the principle of least astonishment, but this is not a "protocol problem". The security impact of UTF-8 headers on email signature systems such as DKIM, S/MIME and OpenPGP is discussed in RFC 4952 section 9. A subsequent document [I-D.ietf-eai-downgrade] will cover the impact of downgrading on these systems. Abel Expires January 10, 2009 [Page 11] Internet-Draft I18N Email Headers July 2008 6. IANA considerations IANA is asked to register the message/global MIME type using the registration form contained in Section 4.4. 7. Acknowledgements This document incorporates many ideas first described in Internet Draft form by Paul Hoffman, although many details have changed from that earlier work. The author especially thank Jeff Yeh for their efforts and contributions on editing previous versions. Most of the content of this document is provided by John C Klensin. Also some significant comments and suggestions were received from Charles H. Lindsey, Kari Hurtta, Pete Resnick, Alexey Melnikov, Chris Newman, Yangwoo KO, Yoshiro YONEYA, and other members of the JET team and were incorporated into the document. The editor is much great thanks to their contribution sincerely. 8. Edit history This section is used for tracking the update of this document. Will be removed after finalize. 8.1. draft-ietf-eai-utf8header-12 1. Sentences modified 2. Update [RFC2045] into the Abstract 3. Update security mechanisms descriptions in Section 5 8.2. draft-ietf-eai-utf8header-11 1. Sentences modified 8.3. draft-ietf-eai-utf8header-10 1. Revise some paragraphs 2. Correct typos of ABNF 3. Note and of 2822bis 4. Fixed some idnits warnning Abel Expires January 10, 2009 [Page 12] Internet-Draft I18N Email Headers July 2008 8.4. draft-ietf-eai-utf8header-09 1. Delete Section 5 (Addtional Issues) 2. Correct two typos of ABNF 3. Refine normalization issue to refer to [RFC5198] 4. Note and of 2822bis 5. Revise Section 6 8.5. draft-ietf-eai-utf8header-08 1. Sentences modified 8.6. draft-ietf-eai-utf8header-07 1. Modify subtype message/utf8smtp to message/global 2. Acknowledgements revise 8.7. draft-ietf-eai-utf8header-06 1. ABNF revise. 2. Sentences modified 3. Add paragraph in Section 5 4. Add paragraph in Section 1.2 5. Modify Section 4.6 8.8. draft-ietf-eai-utf8header-05 1. ABNF revise. 2. Remove original the section 4 (Pre-requirement) 3. Add UTF8SMTP message (Section 4.6) 8.9. draft-ietf-eai-utf8header-04 1. ABNF revise. 2. Modify uFor description in Section 4.5 8.10. draft-ietf-eai-utf8header-03 1. Editrial changes on terms and english. 2. ABNF revise. 3. addr-spec change, put ALT-ADDRESS inside "<" and ">" quote with "<" and ">". 4. Remove the "Header-Type" header. 5. Add uFor description in Section 4.5 6. Remove the content in IANA considerations since "Header-Type" is removed. Abel Expires January 10, 2009 [Page 13] Internet-Draft I18N Email Headers July 2008 8.11. draft-ietf-eai-utf8header-02 1. Editrial changes on terms and english. 2. Change the header name "UTF8SMTP" to "Header-Type", and ABNF revise. 3. addr-spec change, put ALT-ADDRESS inside "<" and ">" quote with "[" and "]". 4. IANA considerations section rewrite. 8.12. draft-ietf-eai-utf8header-01 1. ABNF revise. 2. Terminology sync with overview document. 3. addr-spec change, put ALT-ADDRESS inside "<" and ">" quote with "{" and "}". 4. add IANA considerations to register the new 2822 header "UTF8SMTP". 5. add Security considerations about relation of UTF8SMTP address to ALT-ADDRESS. 8.13. draft-ietf-eai-utf8header-00 1. ABNF added. 2. Editrial changes. 3. Sent it as WG document. 8.14. draft-yeh-ima-utf8header-01 1. Section re-arranged. 2. Remove content are not below to this document. 9. References 9.1. Normative References [I-D.ietf-eai-smtpext] Yao, J. and W. MAO, "SMTP extension for internationalized email address", draft-ietf-eai-smtpext-12 (work in progress), April 2008. [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. Abel Expires January 10, 2009 [Page 14] Internet-Draft I18N Email Headers July 2008 [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", RFC 4952, July 2007. [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network Interchange", RFC 5198, March 2008. 9.2. Informative References [I-D.ietf-eai-downgrade] Fujiwara, K. and Y. Yoneya, "Downgrading mechanism for Email Address Internationalization", draft-ietf-eai-downgrade-07 (work in progress), March 2008. [I-D.ietf-eai-imap-utf8] Resnick, P. and C. Newman, "IMAP Support for UTF-8", draft-ietf-eai-imap-utf8-03 (work in progress), April 2008. [I-D.ietf-eai-pop] Newman, C. and R. Gellens, "POP3 Support for UTF-8", draft-ietf-eai-pop-03 (work in progress), February 2008. [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. Abel Expires January 10, 2009 [Page 15] Internet-Draft I18N Email Headers July 2008 Author's Address Abel Yang (editor) TWNIC 4F-2, No. 9, Sec 2, Roosvelt Rd. Taipei, 100 Taiwan Phone: +886 2 23411313 ext 505 Email: abelyang@twnic.net.tw Abel Expires January 10, 2009 [Page 16] Internet-Draft I18N Email Headers July 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Abel Expires January 10, 2009 [Page 17]