Email Address Internationalization Y. YONEYA, Ed. (EAI) K. Fujiwara, Ed. Internet-Draft JPRS Expires: December 28, 2006 Jun 26, 2006 Downgrading mechanism for Email Address Internationalization (EAI) draft-ietf-eai-downgrade-01.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 December 28, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract Traditional mail systems handle only US-ASCII characters in SMTP envelope and mail headers. The Email Address Internationalization (EAI) is implemented by allowing UTF-8 characters in SMTP envelope and mail headers. To deliver Non-ASCII mail address through EAI incompliant environment, some sort of converting mechanism (i.e. downgrading) is required. This document describes requirements for downgrading, SMTP session downgrading, header downgrading and implementation consideration. YONEYA & Fujiwara Expires December 28, 2006 [Page 1]
Internet-Draft EAI Downgrade Jun 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Downgrade Requirements . . . . . . . . . . . . . . . . . . . . 3 3.1. Timing and conditions of downgrading . . . . . . . . . . . 3 3.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4 4. SMTP Downgrading . . . . . . . . . . . . . . . . . . . . . . . 4 5. SMTP DATA/Header downgrading . . . . . . . . . . . . . . . . . 5 5.1. No header downgrading . . . . . . . . . . . . . . . . . . 6 5.2. Downgrading with MIME encapsulation . . . . . . . . . . . 6 5.2.1. Downgrading with MIME encapsulation example . . . . . 7 5.3. Header conversion . . . . . . . . . . . . . . . . . . . . 8 5.3.1. Downgrading address headers . . . . . . . . . . . . . 9 5.3.2. Header conversion example . . . . . . . . . . . . . . 10 6. Implementation consideration . . . . . . . . . . . . . . . . . 12 6.1. MUA . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2. MDA Requirements . . . . . . . . . . . . . . . . . . . . . 12 7. Security considerations . . . . . . . . . . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 10. Normative References . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 YONEYA & Fujiwara Expires December 28, 2006 [Page 2]
Internet-Draft EAI Downgrade Jun 2006 1. Introduction Traditional mail systems which are defined by [RFC2821] and [RFC2822] allow US-ASCII characters in SMTP envelope and mail headers in body part. The EAI proposal [EAI-Overview],[EAI-UTF8], [EAI-SMTPext] allows UTF-8 characters in SMTP envelope and mail headers in body part. Carrying Non-ASCII mail address from sender to recipients requires all components on the mail delivery route are EAI compliant. Otherwise Non-ASCII mail address can't be delivered. To solve the problem, this document describes downgrading mechanism that enables delivering Non-ASCII mail address by converting it to corresponding US-ASCII representation on current mail delivery system. Not only SMTP envelope, but also UTF-8 characters in mail headers MUST be converted to US-ASCII. Downgrading in EAI consists from following two parts: o SMTP session downgrading o header downgrading Decoding downgraded envelope/message is called 'Upgrading' in this document. Each downgrading mechanism has corresponding upgrading mechanism. In this document, requirements for downgrading is described in section Section 3, SMTP session downgrading is described in Section 4, and mail header downgrading is described in Section 5. 2. Terminology Terminology for this document is defined in [EAI-Overview]. In this document, "algorithmic address" is an US-ASCII address which is generated by algorithmic method. 3. Downgrade Requirements 3.1. Timing and conditions of downgrading This section describes timing and conditions of downgrading. o Timing: SMTP client detects that SMTP server doesn't support "IEmail" option at EHLO. [EAI-SMTPext] o Conditions: SMTP client detects that UTF-8 is included in the SMTP envelope or mail headers in the SMTP DATA. YONEYA & Fujiwara Expires December 28, 2006 [Page 3]
Internet-Draft EAI Downgrade Jun 2006 Note: If the i-Email header exists, downgrading will be performed. If UTF-8 characters exist in mail headers without the i-Email header, this is a protocol error, and handling of this situation is outside the scope of this specification. 3.2. Requirements 1. Downgrading must be performed only once. 2. Upgrading must be performed at minimized place such as final destination like recipient MUA. 3. Downgrading and upgrading must be automated. 4. Downgrading and upgrading should be easy and lightweight as it is possible to do with MTA like 8BITMIME encapsulation. 5. Downgrade and upgrade method must be defined clearly. 6. Downgrading and upgrading should preserve all header information. 7. Downgrading must support SPF and DKIM. 8. Downgrading occurrence must be recorded. 4. SMTP Downgrading Downgrading MUST be performed in each SMTP session. Target of downgrading elements in SMTP envelope are below: o MAIL FROM: o RCPT TO: Downgrading in SMTP envelope uses ALT-ADDR and ATOMIC option proposed in [EAI-SMTPext]. Downgrading is possible only when a mail sender's MUA appends ALT- ADDR or ATOMIC option to all Non-ASCII envelope addresses to denote their alternative US-ASCII address. When MUA/MTA is transferring mail and finding its envelope is Non- ASCII, it MUST decide to bounce or downgrade if receiving MTA is EAI incompliant. Both ALT-ADDR parameter and ATOMIC parameter is specified in one envelope from/to, use ALT-ADDR parameter and ignore ATOMIC parameter. MTA generates alternative US-ASCII address when ALT-ADDR option is not specified and ATOMIC is "y". Further, even if no downgrading is performed for envelope from/to, MUA/MTA MUST downgrade mail headers including UTF-8 or bounce. This is described in next section. YONEYA & Fujiwara Expires December 28, 2006 [Page 4]
Internet-Draft EAI Downgrade Jun 2006 Algorithmic address generation method is below: domain-part: Punycode/IDNA [RFC3490] local-part: Punycode[RFC3492] without normalization. Prefix MUST be assigned by IANA (which is not "xn--"). MTA replaces Non-ASCII mail address with specified or generated alternative US-ASCII address. Then appends replaced information with EAI-Downgraded-From and EAI-Downgraded-To header in mail header (outgoing SMTP DATA). EAI-Downgraded-From: <Non-ASCII,ATOMIC> <US-ASCII> EAI-Downgraded-From: <Non-ASCII,US-ASCII> <US-ASCII> EAI-Downgraded-To: <Non-ASCII,ATOMIC> <US-ASCII> EAI-Downgraded-To: <Non-ASCII,US-ASCII> <US-ASCII> Note that when downgrading, not to disclose whole recipient address, MUA/MTA SHOULD make SMTP connection per each recipient address. Also note that by appending EAI-Downgraded-From/To headers, MUA/MTA MUST perform SMTP DATA/Header downgrading. This is described in next section. Downgraded local-part is parsed only in MDA. MDA delivers the mail to final mailbox. Case study: SPF check SPF checks domainname of the envelope from and smtp connection IP address. If ALT-ADDR domainname is Punycode/IDNA form of Non-ASCII domainname, it will be compatible with current SPF. In this case, SPF check will be performed correctly. Otherwise, more detailed consideration is required. 5. SMTP DATA/Header downgrading In this section, three methods for SMTP DATA/Header downgrading is proposed. Working group should select one. o No header downgrading o Encapsulating whole SMTP DATA o Translating each header Target and non-target of downgrading elements in mail headers (SMTP data) are below: YONEYA & Fujiwara Expires December 28, 2006 [Page 5]
Internet-Draft EAI Downgrade Jun 2006 Originator address(es): Non-ASCII mail addresses in From, Reply-To, Sender and their Resent- headers MUST be target of downgrading. Destination address(es): Non-ASCII mail addresses in To, CC, Bcc and their Resent- headers MUST be target of downgrading. IDs: IDs such as Message-ID, Date, In-Reply-To and References MUST NOT be target of downgrading. Trace headers: Received headers which contains Non-ASCII mail addresses MUST be target of downgrading. other headers: UTF-8 in other headers MUST be target of downgrading. Rewriting Received header is prohibited in [RFC2821] Section 4.4 Trace field. But downgrading may be considered as the 'Mail Gatewaying' which is described in [RFC2821] Section 3.8. If it is true, these downgrading methods are acceptable. 5.1. No header downgrading Most MTAs support 8bit characters in mail headers. Currently, mail systems in some countries or languages use raw 8bit header value in their local encoding. This method does not care about using UTF-8 headers in existing mail systems. Pros: * Easy to implement. Cons: * This method may break existing mail infrastructure. 5.2. Downgrading with MIME encapsulation This downgrading method requires new MIME 'Content-Type:' which express EAI. This document assumes 'Content-Type: Message/EAI' existence. Downgrading: * If mail header contains UTF-8 data, downgrade whole message to be MIME encoded. Whole message becomes new MIME part (Message/ EAI). * Message-ID, Subject, Date headers are copied from original header. * From header is generated with downgraded Envelope-from. * To header is generated with single downgraded Envelope-to. * If Subject header contains UTF-8, it is replaced to a certain message or encoded by MIME [RFC2047]. * Message-ID, Date headers are preserved. As a result, new body contains one new MIME part (Message/EAI). YONEYA & Fujiwara Expires December 28, 2006 [Page 6]
Internet-Draft EAI Downgrade Jun 2006 Upgrading: * If mail message contains only one MIME part and its Content- Type is 'Message/EAI', it may be a downgraded message. To check if it is a downgraded message, compare mail body's message-id and MIME part's message-id. If message-ids are the same, it is a downgraded message. Then, treat MIME part as entire mail message. * When checking trace field, checker SHOULD check Received header both in wrapping headers and headers in encapsulated part. Case study: DKIM DKIM checker performs upgrading the downgraded message first. Pros: * MTA does not need to decode each header carefully. * Whole headers can be submitted AS IS. Cons: * Non-ASCII from/to can not distinguish from downgraded mail headers. * EAI incompliant MUA can not treat any downgraded mail. [[Reference to [EAI-Scenarios] and evaluation of each case should be described here.]] 5.2.1. Downgrading with MIME encapsulation example YONEYA & Fujiwara Expires December 28, 2006 [Page 7]
Internet-Draft EAI Downgrade Jun 2006 Downgrading example Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: Multipart/Mixed; boundary="--Next_Part(unique_string)--" Content-Transfer-Encoding: 8bit Subject: DOWNGRADED_SUBJECT From: <US-ASCII_FROM> To: <US-ASCII_TO> Date: DATE ----Next_Part(unique_string)-- Content-Type: Message/EAI Content-Transfer-Encoding: 8bit Content-Disposition: inline EAI-Downgraded-From: <Non-ASCII,ATOMIC> <US-ASCII_FROM> EAI-Downgraded-To: <Non-ASCII,ATOMIC> <US-ASCII_TO> Received: ... Received: ... Message-Id: MESSAGE_ID Mime-Version: 1.0 Subject: UTF-8_SUBJECT From: <Non-ASCII,ATOMIC> To: <Non-ASCII,ATOMIC> Date: DATE MAIL_BODY ----Next_Part(unique_string)---- 5.3. Header conversion Define conversion method to US-ASCII for each header which may contain Non-ASCII characters. Each header has its own downgrading method. To preserve all header information, define generic encapsulation header: "Downgraded: HeaderName: HeaderValue". The header value is encoded by [RFC2047] with UTF-8 tag. Downgrading: * For all headers, check if the header contains UTF-8 characters. * Encapsulate 'i-Email' header in Downgraded header. YONEYA & Fujiwara Expires December 28, 2006 [Page 8]
Internet-Draft EAI Downgrade Jun 2006 * If the header contains UTF-8 characters, + If the header is an address header which is described in Section 5.3.1, - Preserve the header in 'Downgraded' header. - Downgrade the header defined in Section 5.3.1. + The other header case, encode the header by [RFC2047] with UTF-8 tag. Upgrading: * If the mail has 'Downgraded' headers, the mail is a downgraded EAI mail message. * Decode all 'Downgraded' header. + Decode header value field string which is [RFC2047] encoded. + If the header is address headers described in Section 5.3.1, - Apply address header downgrading to the decoded header. - Remove the header line which is same to the downgraded line. + Remove the 'Downgraded' header. + Add decoded header to mail header. "HeaderName: HeaderValue". * If each mail header has [RFC2047] encoded part and which encoding is "UTF-8", it is a downgraded header, so decode it. Pros: * EAI incompliant MUA displays the downgraded mail body except original Non-ASCII mail addresses. * EAI incompliant MUA displays and handles the sender specified or algorithmic address. * EAI compliant MUA displays and handles original headers. Cons: * Implementation and processing cost is higher than 'Header Encapsulation' defined in Section 5.2 because MUA/MTA must parse each header and encode it by defined method. * Hard to preserve whole information AS IS. The address headers are preserved but the other headers which is [RFC2047] encoded with UTF-8 tag are not distinguished that it is downgraded or it is encoded by sender's MUA. Therefore, to check DKIM requires special consideration. [[Reference to [EAI-Scenarios] and evaluation of each case should be described here.]] 5.3.1. Downgrading address headers This section targets From, Sender, Reply-To, To, CC, BCC, Resent- From, Resent-To, Resent-CC, Resent-Bcc, Resent-sender headers which contains Originator/Destination address(es). The header value is composed of single or multiple mailbox/angle-addr YONEYA & Fujiwara Expires December 28, 2006 [Page 9]
Internet-Draft EAI Downgrade Jun 2006 fields defined in [EAI-UTF8]. If the header contains UTF-8 characters, downgrading method is follows. 1. Extract every field and downgrade mailbox/angle-addr described below. 2. By mailbox/angle-addr downgrading, if the field became empty, the field should be removed. 3. If all header field is removed, remove the header. 4. If From header is removed, generate new From header from envelope-from address. EAI angle-addr defined in [EAI-UTF8] consists of 4 forms. Downgrading method is defined for each form. 1. <Non-ASCII> Non-ASCII mail address without ALT-ADDR and ATOMIC parameter case, remove this angle-addr. 2. <Non-ASCII,US-ASCII> Non-ASCII mail address with sender-specified US-ASCII address case, replace it as <US-ASCII>. 3. <Non-ASCII,ATOMIC> Non-ASCII mail address with ATOMIC parameter case, generate the algorithmic address from Non-ASCII mail address and replace it as <ALG-ASCII>. 4. <US-ASCII> US-ASCII mail address case, preserve it. "mailbox" is defined as "DISPLAY NAME angle-addr" in [EAI-UTF8]. The "DISPLAY NAME" field should be encoded by [RFC2047] with UTF-8 tag, if necessary. If the angle-addr is removed, remove the field including "DISPLAY NAME". 5.3.2. Header conversion example YONEYA & Fujiwara Expires December 28, 2006 [Page 10]
Internet-Draft EAI Downgrade Jun 2006 Original EAI message i-Email: 1.0 Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: UTF-8_SUBJECT From: <NON-ASCII-FROM,ASCII-FROM> To: <NON-ASCII-TO,ASCII-TO> CC: <NON-ASCII-CC,ASCII-CC> Date: DATE MAIL_BODY SMTP downgrading adds EAI-Downgraded-From, EAI-Downgraded-To headers. EAI-Downgraded-From: <Non-ASCII,DOWNGRADED_FROM> <DOWNGRADED_FROM> EAI-Downgraded-To: <Non-ASCII,DOWNGRADED_TO> <DOWNGRADED_TO> Result of the header conversion downgrading. EAI-Downgraded-From: MIME(<Non-ASCII,DOWNGRADED_FROM>) <DOWNGRADED_FROM> EAI-Downgraded-To: MIME(<Non-ASCII,DOWNGRADED_TO>) <DOWNGRADED_TO> Downgraded: i-Email: 1.0 Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: MIME(UTF-8_SUBJECT) Downgraded: From: MIME(<NON-ASCII-FROM,ASCII-FROM>) From: <ASCII-FROM> Downgraded: To: MIME(<NON-ASCII-TO,ASCII-TO>) To: <ASCII-TO> Downgraded: CC: MIME(<NON-ASCII-CC,ASCII-CC>) CC: <ASCII-CC> Date: DATE MAIL_BODY MIME() stands for [RFC2047] encoding. YONEYA & Fujiwara Expires December 28, 2006 [Page 11]
Internet-Draft EAI Downgrade Jun 2006 6. Implementation consideration 6.1. MUA EAI compliant MUA MUST implement downgrading mechanism for sending. MUA MAY encode UTF-8 in Subject header with the same encoding of body part while downgrading. EAI compliant MUA MUST upgrade downgraded mail and MUST show Non- ASCII mail addresses on display. 6.2. MDA Requirements This section describes downgrading in MDA. 1. MDA MUST NOT upgrade. 2. Perform downgrading for each Storage/Back-end-Process. If and only if MDA knows recipient's MUA is EAI compliant, then no downgrading is performed. 3. If MDA detects that SMTP recipient address is an algorithmic address, then MDA MUST decode it and perform the same processing as if it were Non-ASCII mail address. MDA MAY normalize or canonicalize local-part before processing it. 7. Security considerations See the extended security considerations discussion in [EAI-Overview] 8. IANA Considerations To distinguish downgraded Non-ASCII mail addresses in ACE form, it MUST have ACE-Prefix. The ACE-Prefix MUST differ from IDNA ACE- Prefix to avoid possible confusion. IANA will assign Non-ASCII mail address ACE-Prefix when RFC is published. 9. Acknowledgements John Klensin, Harald Alvestrand, Chris Newman, Charles Lindsey, Marcos Sanz, Alexey Melnikov, and JET members. 10. Normative References [EAI-Overview] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", draft-ietf-eai-framework-01 YONEYA & Fujiwara Expires December 28, 2006 [Page 12]
Internet-Draft EAI Downgrade Jun 2006 (work in progress). [EAI-SMTPext] Yao, J., Ed., "SMTP extension for internationalized email address", draft-ietf-eai-smtpext-00 (work in progress), Febrary 2006. [EAI-Scenarios] Alvestrand, H., "Internationalized Email Addresses: Scenarios", draft-ietf-eai-scenarios-00 (work in progress), May 2006. [EAI-UTF8] Yeh, J., "Internationalized Email Headers", draft-yeh-ima-utf8headers-01 (work in progress), February 2006. [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)", RFC 3492, March 2003. YONEYA & Fujiwara Expires December 28, 2006 [Page 13]
Internet-Draft EAI Downgrade Jun 2006 Authors' Addresses Yoshiro YONEYA (editor) JPRS Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda Chiyoda-ku, Tokyo 101-0065 Japan Phone: +81 3 5215 8451 Email: yone@jprs.co.jp Kazunori Fujiwara (editor) JPRS Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda Chiyoda-ku, Tokyo 101-0065 Japan Phone: +81 3 5215 8451 Email: fujiwara@jprs.co.jp YONEYA & Fujiwara Expires December 28, 2006 [Page 14]
Internet-Draft EAI Downgrade Jun 2006 Intellectual Property Statement 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. Disclaimer of Validity 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 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. Copyright Statement Copyright (C) The Internet Society (2006). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. YONEYA & Fujiwara Expires December 28, 2006 [Page 15]
