Email Address Internationalization Y. YONEYA, Ed. (EAI) K. Fujiwara, Ed. Internet-Draft JPRS Intended status: Experimental July 6, 2007 Expires: January 7, 2008 Downgrading mechanism for Email Address Internationalization draft-ietf-eai-downgrade-04.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 7, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract Traditional mail systems handle only US-ASCII characters in SMTP envelope and mail header fields. The Email Address Internationalization (UTF8SMTP) allows UTF-8 characters in SMTP envelope and mail header fields. To deliver internationalized Email messages to/via UTF8SMTP non-compliant environment, some sort of converting mechanism is required. This document describes downgrading mechanism for Email Address Internationalization. YONEYA & Fujiwara Expires January 7, 2008 [Page 1] Internet-Draft UTF8SMTP Downgrade July 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. New header fields definition . . . . . . . . . . . . . . . . . 4 4. SMTP Downgrading . . . . . . . . . . . . . . . . . . . . . . . 5 5. Email header fields downgrading . . . . . . . . . . . . . . . 6 6. MIME body part headers downgrading . . . . . . . . . . . . . . 9 7. Security considerations . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 10. Change History . . . . . . . . . . . . . . . . . . . . . . . . 11 10.1. draft-yoneya-ima-downgrade: Version 00 . . . . . . . . . 11 10.2. draft-yoneya-ima-downgrade: Version 01 . . . . . . . . . 11 10.3. draft-ietf-eai-downgrade: Version 00 . . . . . . . . . . 11 10.4. draft-ietf-eai-downgrade: Version 01 . . . . . . . . . . 12 10.5. draft-ietf-eai-downgrade: Version 02 . . . . . . . . . . 12 10.6. draft-ietf-eai-downgrade: Version 03 . . . . . . . . . . 12 10.7. draft-ietf-eai-downgrade: Version 04 . . . . . . . . . . 12 11. Normative References . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. Displaying downgraded message . . . . . . . . . . . . 14 A.1. Displaying technique 1 . . . . . . . . . . . . . . . . . 14 A.2. Displaying technique 2 . . . . . . . . . . . . . . . . . 14 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 14 B.1. Downgrading example 1 . . . . . . . . . . . . . . . . . . 14 B.2. Displaying example (Displaying technique 1) . . . . . . . 17 B.3. Displaying example (Displaying technique 2) . . . . . . . 17 B.4. Downgrading example 2 . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 Intellectual Property and Copyright Statements . . . . . . . . . . 22 YONEYA & Fujiwara Expires January 7, 2008 [Page 2] Internet-Draft UTF8SMTP Downgrade July 2007 1. Introduction Traditional mail systems which are defined by [RFC2821] and [RFC2822] allow US-ASCII characters in SMTP envelope and mail header field values. The UTF8SMTP proposals [I-D.ietf-eai-framework], [I-D.ietf-eai-utf8headers] and [I-D.ietf-eai-smtpext] allow UTF-8 characters in SMTP envelope and mail header field values. Delivering non-ASCII mail addresses from a sender to recipients requires all components on the mail delivery route are UTF8SMTP 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 addresses to traditional mail system by converting them to corresponding US-ASCII representation. And more, [I-D.ietf-eai-utf8headers] expands that mail header fields and MIME header fields are allowed to use any UTF-8 characters. This downgrading mechanism targets mail header fields and MIME header fields to be converted to US-ASCII only to send to UTF8SMTP non- compliant receivers. [I-D.ietf-eai-smtpext] section 2.2 defines when downgrading occurs. Mail clients (MUAs, MSAs, MTAs) try to deliver Email messages to SMTP servers by static setting or DNS MX resource records resolution. If the SMTP client has an UTF8SMTP envelope or an UTF8SMTP message and the SMTP client detects that SMTP server doesn't support "UTF8SMTP" option at EHLO, then the SMTP client MUST NOT send the UTF8SMTP envelope or UTF8SMTP message to the SMTP server. The section shows 4 choices. The second choice "reject or generate a notification of non-deliverability" is always allowed. The fourth choice is downgrading. Downgrading may be implemented in MUAs, MSAs, MTAs, MDAs which generates or receives UTF8SMTP envelopes or UTF8SMTP messages and may send them to non-UTF8SMTP compliant systems. This document tries to define the downgrading process clearly and it preserves the original information as much as possible. Downgrading in UTF8SMTP consists of the following four parts: o New header fields definition o SMTP downgrading o Email header fields downgrading o MIME header fields downgrading Before sending to traditional SMTP server, the downgrading process need to perform SMTP downgrading, Email header fields downgrading, and MIME header fields downgrading. In Section 3, two header fields are introduced. One is "Envelope- YONEYA & Fujiwara Expires January 7, 2008 [Page 3] Internet-Draft UTF8SMTP Downgrade July 2007 Downgraded:", it preserves the original envelope information. The other is "Downgraded:", it preserves the original header fields which contains non-ASCII email addresses or which does not have clear downgrading definition. The SMTP downgradin is described in Section 4. It generates US-ASCII only envelope information from an UTF8SMTP envelope. The Email header fields downgrading is described in Section 5. It generates US-ASCII only header fields. The MIME header fields are expanded in [I-D.ietf-eai-utf8headers]. The MIME header fields downgrading is described in Section 6. It generates US-ASCII only MIME header fields. 2. Terminology The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY" in this document are to be interpreted as described in RFC 2119 [RFC2119]. All specialized terms used in this specification are defined in the EAI overview [I-D.ietf-eai-framework] or in [RFC2821][RFC2822], MIME documents [RFC2045] [RFC2047] [RFC2183] [RFC2231]. The terms "ASCII address", "internationalized email address", "non-ASCII address", "i18mail address", "UTF8SMTP", "message" and "mailing list" are used with the definitions from [I-D.ietf-eai-framework] document. This document depends on [I-D.ietf-eai-smtpext], [I-D.ietf-eai-utf8headers], and [I-D.ietf-eai-dsn]. Key words used in these document are used in this document, too. The term "non-ASCII" is an UTF-8 string which contains at least one non-ASCII character. An "UTF8SMTP envelope" has Email originator/recipient addresses expanded by [I-D.ietf-eai-smtpext] and [I-D.ietf-eai-dsn]. An "UTF8SMTP message" is Email messages expanded by [I-D.ietf-eai-utf8headers]. 3. New header fields definition A generic encapsulation header "Downgraded:" is defined to preserve the original header field. It has two value fields. The former value field holds the original header field name. The latter value YONEYA & Fujiwara Expires January 7, 2008 [Page 4] Internet-Draft UTF8SMTP Downgrade July 2007 field holds the original header field value. Any original header field value is treated as an unstructured value. The latter value field of this header MUST be encoded by [RFC2047] section 5(1) method with charset='UTF-8' same as a 'Subject' header. The header field syntax is specified as follows: fields =/ downgraded downgraded = "Downgraded:" [FWS] field-name ":" unstructured CRLF Encapsulating a header in a Downgraded: header is defined as: 1. Generate new Downgraded: header whose former value is the original header field name and latter value is the original header fleid value. 2. Encode the generated header by [RFC2047] section 5(1) method with charset='UTF-8'. 3. Replace the original header field as the generated header field. Another new header "Envelope-Downgraded:" is defined to preserve SMTP envelope downgraded information. SMTP envelope downgraded information consists of the original non-ASCII address and the downgraded all-ASCII address. The non-ASCII address is encoded by [RFC2047] with charset='UTF-8'. The header field syntax is specified as follows: fields =/ edowngraded edowngraded = "Envelope-Downgraded:" [FWS] edowngraded-field ":" [FWS] "<" uPath ">" [FWS] "<" Mailbox ">" [FWS] CRLF edowngraded-field = "From" / "To" Original non-ASCII address is defined in [I-D.ietf-eai-smtpext]. is defined in [RFC2821], section 4.1.2. The "Envelope-Downgraded:" header field is encoded by [RFC2047] in the downgraded message. 4. SMTP Downgrading Target of downgrading elements in SMTP envelope are below: o MAIL FROM: o RCPT TO: o ORCPT parameter Downgrading in SMTP envelope uses ALT-ADDRESS parameter defined in [I-D.ietf-eai-smtpext]. An address is downgradable if the address is YONEYA & Fujiwara Expires January 7, 2008 [Page 5] Internet-Draft UTF8SMTP Downgrade July 2007 US-ASCII address or the address has US-ASCII address specified by ALT-ADDRESS parameter. If each recipient address and the return address is downgradable, the SMTP to the recipient is downgradable. Even if no downgrading is performed for envelope from/to, MUA/MTA MUST downgrade message header fields and MIME header fields in the message body including non-ASCII characters. This is described in Section 5 and Section 6. MTA replaces non-ASCII mail address with specified alternative US- ASCII address when downgrading. Before replacing, decode the ALT- ADDRESS parameter value because it is encoded as xtest [RFC3461]. Also MTA preserves original information using "Envelope-Downgraded" header defined in Section 3 with From or To field name. The non- ASCII mail addresses are encoded by [RFC2047] and put into "Envelope- Downgraded" header. Not to disclose whole recipient addresses, MUA/MTA MUST NOT add "Envelope-Downgraded: To:" header if the SMTP downgrading targets multiple recipients. See Section 7 for more detail. While the recipient address downgrading, the "RCPT TO" command may have an ORCPT parameter. The ORCPT parameter is used for DSN [RFC3461]. If the ORCPT parameter contains "utf-8" address type address and the address contains non-ASCII characters, the ORCPT parameter MUST be converted to utf-8-addr-xtext form or utf-8-addr- unitext form which is described in [I-D.ietf-eai-dsn]. 5. Email header fields downgrading This section defines conversion method to US-ASCII for each header field which may contain non-ASCII characters. Header fields are listed in [RFC4021]. If the whole mail header field does not contain non-ASCII characters, email header field downgrading is not required. If the header field contains non-ASCII characters, convert the header field. Each header field's downgrading method is described below. o Downgrading Address header fields From: Sender: YONEYA & Fujiwara Expires January 7, 2008 [Page 6] Internet-Draft UTF8SMTP Downgrade July 2007 Reply-To: To: Cc: Bcc: Resent-From: Resent-Sender: Resent-To: Resent-Cc: The header field value is composed of single or multiple / fields defined in [I-D.ietf-eai-utf8headers]. If the header has no or which contains non-ASCII characters, only "display-name" part or comments contain non-ASCII characters, the "display-name" or comments are encoded by [RFC2047] with charset='UTF-8'. Otherwise, preserve the header field in "Downgraded:" header, generate US-ASCII only address header, and replace the original header field with the generated US-ASCII only header field. New header generation method are shown in below. Extract every field and downgrade each // . If the non-ASCII address is in form, then rewrite it as "Internationalized Address utf8-addr-spec-encoded Removed:;". "utf8-addr-spec" is encoded to "utf8-addr-spec- encoded" by [RFC2047]. The field may contain multiple fields. The fields are encoded by [RFC2047] with charset='UTF-8', if necessary. is defined as "display-name " in [I-D.ietf-eai-utf8headers]. The "display-name" field is encoded by [RFC2047] with charset='UTF-8', if necessary. The may contain comments. Before processing, remove comments from the . UTF8SMTP defined in [I-D.ietf-eai-utf8headers] consists of 3 forms. Downgrading method is defined for each form. * is used as is. * Non-ASCII mail address without sender-specified US-ASCII address is replaced as YONEYA & Fujiwara Expires January 7, 2008 [Page 7] Internet-Draft UTF8SMTP Downgrade July 2007 "Internationalized Address non-ASCII-encoded Removed:;". non-ASCII address is encoded to "non-ASCII-encoded" by [RFC2047]. * > Non-ASCII mail address with sender-specified US-ASCII address MUST be replaced as "display-name ". o Downgrading Non-ASCII in comments Date: Message-ID: In-Reply-To: References: Resent-Date: Resent-Message-ID: MIME-Version: Content-ID: These header fields do not contain non-ASCII characters except in comments. If the header contains UTF-8 characters in comments, encode the header by [RFC2047] with charset='UTF-8'. o Trace header Received: If the FOR clause contains non-ASCII addresses, remove the FOR clause in the header. The other part does not contain non-ASCII values. o MIME Content header Content-Type: Content-Disposition: Encode the header by [RFC2231] with charset='UTF-8'. o Unstructured text headers and structured text headers Subject: Comments: Keywords: Content-Description: Encode the header by [RFC2047] with charset='UTF-8'. YONEYA & Fujiwara Expires January 7, 2008 [Page 8] Internet-Draft UTF8SMTP Downgrade July 2007 o URI headers List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: If the header contains UTF-8 characters in comments, encode the header by [RFC2047] with charset='UTF-8'. If the header contains UTF-8 characters in URI, Encode the URI by [RFC3987]. o Other target headers All other headers which contains non-ASCII characters are preserved in Downgraded: header and removed. o ASCII only headers Content-Transfer-Encoding: This header is not target of downgrading. Downgraded header fields should be inserted or replaced at the same position of the original header field. 6. MIME body part headers downgrading MIME body part header fields may contain non-ASCII characters [I-D.ietf-eai-utf8headers]. This section defines conversion method to US-ASCII for each MIME header field which may contain non-ASCII characters. Parse the message body's MIME structure for all level and check all MIME header fields whether contains non-ASCII characters. If the header contains non-ASCII characters in the header value, the header is a target of the MIME body part headers downgrading. Each MIME header field's downgrading method is described below: Content-ID: The Content-ID: header does not contain non-ASCII characters except in comments. If the header contains UTF-8 characters in comments, encode the header by [RFC2047] with charset='UTF-8'. YONEYA & Fujiwara Expires January 7, 2008 [Page 9] Internet-Draft UTF8SMTP Downgrade July 2007 Content-Type: Content-Disposition: Encode the header by [RFC2231] with charset='UTF-8'. Content-Description: Encode the header by [RFC2047] with charset='UTF-8'. Content-Transfer-Encoding: This header does not contain non-ASCII characters. 7. Security considerations o Rewriting headers increases the opportunities for undetected spoofing. o Recipients addresses can be undisclosed if those addresses are listed on Bcc or group address. Those undisclosed addresses are used only in the Envelope. Copying information from the Envelope into headers creates some risk of inadvertent information disclosure (not just about addresses). o It is likely that the techniques suggested here will invalidate methods that depend on signatures over headers or the envelope. "Issues" does talk about that, but, because this document strongly implies that one can downgrade and then upgrade again with no risk of loss of information, the topic should be explored further. o Many gateways and servers on the Internet will discard headers with which they are not familiar. To the extent to which the downgrade procedures depend on new headers (e.g., "Downgraded") to avoid information loss, then the risk of having those headers dropped and its implications must be identified. In particular, it appears to me that, if the Downgraded headers are dropped, there is no possibility of reconstructing the original information at any point (before, during, or after delivery). See "Security considerations" section in [I-D.ietf-eai-framework] for more discussion. 8. IANA Considerations IANA is requested to register the following header fields in the Permanent Message Header Field Repository, in accordance with the procedures set out in [RFC3864]. YONEYA & Fujiwara Expires January 7, 2008 [Page 10] Internet-Draft UTF8SMTP Downgrade July 2007 Header field name: Downgraded Applicable protocol: mail Status: experimental Author/change controller: IETF Specification document(s): This document (Section 3) Header field name: Envelope-Downgraded Applicable protocol: mail Status: experimental Author/change controller: IETF Specification document(s): This document (Section 3) 9. Acknowledgements Significant comments and suggestions were received from John Klensin, Harald Alvestrand, Chris Newman, Charles Lindsey, Marcos Sanz, Alexey Melnikov, Frank Ellermann and JET members. 10. Change History This section is used for tracking the update of this document. Will be removed after finalize. 10.1. draft-yoneya-ima-downgrade: Version 00 o Initial version o Followed draft-yeh-ima-utf8headers-00 and draft-yao-smtpext-00 10.2. draft-yoneya-ima-downgrade: Version 01 o Document structure was changed o Followed draft-yeh-ima-utf8headers-01 and draft-yao-smtpext-02 o Downgrading requirements were added o SMTP DATA encapsulation method was proposed o Downgrading examples was provided 10.3. draft-ietf-eai-downgrade: Version 00 o Followed draft-yeh-ima-utf8headers-01 and draft-ietf-eai-smtpext-00 o No header downgrading method was proposed o Header encapsulation method was proposed YONEYA & Fujiwara Expires January 7, 2008 [Page 11] Internet-Draft UTF8SMTP Downgrade July 2007 10.4. draft-ietf-eai-downgrade: Version 01 o Followed draft-ietf-eai-utf8headers-00 o Header conversion and encapsulation method was merged o Header conversion method was defined in detail 10.5. draft-ietf-eai-downgrade: Version 02 o Followed draft-ietf-eai-utf8headers-01 and draft-ietf-eai-smtpext-01 o Specification about algorithmic generated address is removed o No header downgrading method was removed o SMTP DATA encapsulation method was removed 10.6. draft-ietf-eai-downgrade: Version 03 o Followed draft-ietf-eai-utf8headers-03 and draft-ietf-eai-smtpext-03 o Downgraded: and Envelope-Downgraded: headers definition was added o Mail header downgrading method was refined o Examples in Appendix A were refined 10.7. draft-ietf-eai-downgrade: Version 04 o Followed draft-ietf-eai-utf8headers-06, draft-ietf-eai-smtpext-07 and draft-ietf-eai-dsn-02 o Downgrading requirements and conditions were moved to Introduction. o Descriptions about upgrading were removed. o SPF and DKIM discussion were removed. o Added many header fields downgrading. o Allow address literal rewriting without alternate US-ASCII address in header fields. o Added MIME body part headers downgrading. o Added ORCPT downgrading. 11. Normative References [I-D.ietf-eai-dsn] Newman, C. and A. Melnikov, "International Delivery and Disposition Notifications", draft-ietf-eai-dsn-02 (work in progress), July 2007. [I-D.ietf-eai-framework] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", draft-ietf-eai-framework-05 (work in progress), February 2007. YONEYA & Fujiwara Expires January 7, 2008 [Page 12] Internet-Draft UTF8SMTP Downgrade July 2007 [I-D.ietf-eai-smtpext] Yao, J. and W. Mao, "SMTP extension for internationalized email address", draft-ietf-eai-smtpext-07 (work in progress), June 2007. [I-D.ietf-eai-utf8headers] Yeh, J., "Internationalized Email Headers", draft-ietf-eai-utf8headers-05 (work in progress), April 2007. [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field", RFC 2183, August 1997. [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations", RFC 2231, November 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. [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, September 2004. [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005. [RFC4021] Klyne, G. and J. Palme, "Registration of Mail and MIME YONEYA & Fujiwara Expires January 7, 2008 [Page 13] Internet-Draft UTF8SMTP Downgrade July 2007 Header Fields", RFC 4021, March 2005. Appendix A. Displaying downgraded message Displaying downgraded message is mostly retrieved by MIME decoding [RFC2047][RFC2231]. Result of MIME decoding, downgraded address header fields and undefined header fields are still in Downgraded: headers, but it is MIME decoded. This decoded Downgraded: headers contain the original headers and the recipient can read them. But the recipient's MUA cannot use the original header fields automatically. Additionally, MUAs can decode Downgraded: header. It is described in Appendix A.1 and Appendix A.2. A.1. Displaying technique 1 MUA can remove 'Downgraded:' from decoded 'Downgraded:' header fields. With this technique, The address header fields may be displayed twice, one is ASCII-only downgraded header field and the other is from decoded Downgraded: header. A.2. Displaying technique 2 MUA can decode and regenerate headers which contains the original non-ASCII addresses. It is described below: o For each Downgraded: header, generate new header which field-name is the second field of the Downgraded: header and the header value is the third field of the Downgraded: header. * If the header is an address header described in Section 5, + Generate ASCII only header defined in Section 5 from the decoded header. + Remove the header field which is the same with the generated ASCII only header from the header fields. If the headers contain [RFC2047] encoded part, decode it before comparison. Appendix B. Examples B.1. Downgrading example 1 This section shows an SMTP Downgrading example. Consider a downgradable mail message. o The sender address is "NON-ASCII-FROM" which is non-ASCII address. Its ASCII alternative is "ASCII-FROM". YONEYA & Fujiwara Expires January 7, 2008 [Page 14] Internet-Draft UTF8SMTP Downgrade July 2007 o The "To" address is "NON-ASCII-TO" which is non-ASCII address. Its ASCII alternative is "ASCII-TO". o The "CC" address is non-ASCII address "NON-ASCII-CC" without alternative US-ASCII address. o The Subject header is "NON-ASCII-SUBJECT" which contains non-ASCII characters. Original UTF8SMTP message SMTP session MAIL From: ALT-ADDRESS RCPT TO: ALT-ADDRESS RCPT TO: ------------------------------------------------------------- Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: > To: > CC: Date: DATE MAIL_BODY Figure 3: Original UTF8SMTP message In this example, there are two SMTP recipients, one is To:, the other is CC:. In this example, assume the Cc: recipient's MTA supports UTF8SMTP and the To: recipient's MTA does not support UTF8SMTP. The SMTP downgrading treats To: session downgrading. Figure 4 shows SMTP downgraded example. YONEYA & Fujiwara Expires January 7, 2008 [Page 15] Internet-Draft UTF8SMTP Downgrade July 2007 MAIL From: RCPT TO: ------------------------------------------------------------- Envelope-Downgraded: From: Envelope-Downgraded: To: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: > To: > CC: Date: DATE MAIL_BODY Figure 4: SMTP Downgraded UTF8SMTP message After SMTP downgrading, header downgrading is performed. Final downgraded messages are shown in Figure 5. Return-Path header will be added the destination MTA. Result of the header downgrading. Return-Path: Envelope-Downgraded: From: Envelope-Downgraded: To: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: RFC2047(UTF-8_SUBJECT) Downgraded: From: RFC2047(>) From: Downgraded: To: RFC2047(>) To: Downgraded: CC: RFC2047() CC: Internationalized address RFC2047(NON-ASCII-CC) removed:; Date: DATE MAIL_BODY Figure 5: Header downgraded message YONEYA & Fujiwara Expires January 7, 2008 [Page 16] Internet-Draft UTF8SMTP Downgrade July 2007 RFC2047() stands for [RFC2047] encoding. B.2. Displaying example (Displaying technique 1) This example shows MIME decoded message of Figure 5. Result of MIME decoding. Return-Path: Envelope-Downgraded: From: Envelope-Downgraded: To: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: UTF-8_SUBJECT Downgraded: From: > From: Downgraded: To: > To: Downgraded: CC: CC: Internationalized address NON-ASCII-CC removed:; Date: DATE MAIL_BODY Figure 6: MIME decoded message B.3. Displaying example (Displaying technique 2) This example shows displaying process of Appendix A.2 for Figure 5. First, check 'Downgraded:' header existence. Select 'Downgraded:' headers. Downgraded: From: > Downgraded: To: > Downgraded: CC: Figure 7: Displaying technique 2: selecting Downgraded headers YONEYA & Fujiwara Expires January 7, 2008 [Page 17] Internet-Draft UTF8SMTP Downgrade July 2007 Apply address header downgrading to the decoded header. From: To: CC: Internationalized address RFC2047(NON-ASCII-CC) removed:; Figure 8: Displaying technique 2: downgraded decoded Downgraded headers Remove the header line which is the same with the downgraded line. If the headers contain [RFC2047] encoded part, decode it before comparison. Return-Path: Envelope-Downgraded: From: Envelope-Downgraded: To: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: UTF-8_SUBJECT Downgraded: From: > Downgraded: To: > Downgraded: CC: > Date: DATE MAIL_BODY Figure 9: Displaying technique 2: Removing duplicated headers YONEYA & Fujiwara Expires January 7, 2008 [Page 18] Internet-Draft UTF8SMTP Downgrade July 2007 Decode each 'Downgraded' header and replace it with its decoded header. If each mail header has [RFC2047] encoded part and which encoding is "UTF-8", it is a downgraded header, so decode it. Return-Path: Envelope-Downgraded: From: Envelope-Downgraded: To: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: UTF-8_SUBJECT From: > To: > CC: > Date: DATE MAIL_BODY Figure 10: Display technique 2: decoded message As a result, in this simple example, all original header fields are displayed in the original form. B.4. Downgrading example 2 In many cases, the sender wants to use non-ASCII address and the recipient does not support UTF8SMTP and does not have non-ASCII address. o The sender address is "NON-ASCII-FROM" which is non-ASCII address. Its ASCII alternative is "ASCII-FROM". o The "To" address is "ASCII-TO" which is ASCII only. o The Subject header is "NON-ASCII-SUBJECT" which contains non-ASCII characters. YONEYA & Fujiwara Expires January 7, 2008 [Page 19] Internet-Draft UTF8SMTP Downgrade July 2007 Original UTF8SMTP message SMTP session MAIL From: ALT-ADDRESS RCPT TO: ------------------------------------------------------------- Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: > To: Date: DATE MAIL_BODY Figure 11: Original UTF8SMTP message 2 In this example, SMTP session is downgradable. Figure 12 shows SMTP downgraded example. MAIL From: RCPT TO: ------------------------------------------------------------- Envelope-Downgraded: From: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: > To: Date: DATE MAIL_BODY Figure 12: SMTP Downgraded UTF8SMTP message 2 After SMTP downgrading, header downgrading is performed. The downgraded example is shown in Figure 13. YONEYA & Fujiwara Expires January 7, 2008 [Page 20] Internet-Draft UTF8SMTP Downgrade July 2007 Envelope-Downgraded: From: Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: RFC2047(UTF-8_SUBJECT) Downgraded: From: RFC2047(>) From: To: Date: DATE MAIL_BODY Figure 13: Header downgraded message 2 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 January 7, 2008 [Page 21] Internet-Draft UTF8SMTP Downgrade July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). YONEYA & Fujiwara Expires January 7, 2008 [Page 22]