Email Address Internationalization K. Fujiwara (EAI) JPRS Internet-Draft March 9, 2009 Intended status: Experimental Expires: September 10, 2009 Displaying Downgraded Messages for Email Address Internationalization draft-ietf-eai-downgraded-display-01.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 September 10, 2009. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes how to display downgraded messages which originally contain internationalized E-mail addresses or Fujiwara Expires September 10, 2009 [Page 1] Internet-Draft Displaying Downgraded Messages March 2009 internationalized header fields. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Consideration of displaying downgraded message . . . . . . . . 4 4. Displaying downgraded message . . . . . . . . . . . . . . . . 4 5. Security considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 8. Change History . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. draft-fujiwara-eai-downgraded-display: Version 00 . . . . 6 8.2. draft-ietf-eai-downgraded-display: Version 00 . . . . . . 6 8.3. draft-ietf-eai-downgraded-display: Version 01 . . . . . . 6 9. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 7 A.1. Displaying example . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 Fujiwara Expires September 10, 2009 [Page 2] Internet-Draft Displaying Downgraded Messages March 2009 1. Introduction The Email Address Internationalization (UTF8SMTP) extension document set [RFC4952] [RFC5336] [RFC5335] [RFC5337] expands Email address structure, syntax and Email header format. To avoid bouncing internationalized Email messages, the downgrading mechanism [I-D.ietf-eai-downgrade] converts an internationalized message to a traditional Email message when a server in the delivery path does not support the UTF8SMTP extension. The downgraded message is a traditional Email message, except the message has "Downgraded-" header fields. A perfect reverse-function of the downgrading does not exist because the encoding defined in [RFC2047] is not exactly reversible and Received header field downgrading may remove FOR clause information. The restoration of the downgrading should be done once at the final destination of the downgraded message such as MUAs or IMAP servers. This document describes the restoration methods as displaying downgraded messages in MUAs. 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]. Specialized terms used in this specification are defined in the EAI overview [RFC4952] or in [RFC5321][RFC5322], MIME documents [RFC2045] [RFC2047] [RFC2183] [RFC2231]. This document depends on [RFC5335] and [I-D.ietf-eai-downgrade]. 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. The term "address header field" is used for a header field which contains elements which is defined in [RFC5322]. "Address header fields" contain "From", "Sender", "Reply-To", "To", "Cc", "Bcc", "Resent-From", "Resent-Sender", "Resent-To", "Resent-Cc", "Return-Path" header fields. An "UTF8SMTP message" is an Email messages expanded by [RFC5335]. The term "MIME decode" is used for both "encoded-word" decoding defined by [RFC2047] and MIME parameter value decoding defined by [RFC2231]. Fujiwara Expires September 10, 2009 [Page 3] Internet-Draft Displaying Downgraded Messages March 2009 3. Consideration of displaying downgraded message Displaying downgraded message is mostly performed by MIME decoding according to [RFC2047] and [RFC2231]. Result of MIME decoding, the header of the message still contains Downgraded-*: header fields, but the header field bodies are MIME decoded. These decoded "Downgraded-" header fields contain the original header field name and the original header field values. The recipient can read them. But the recipient's MUA cannot use the original header fields automatically. Additionally, MUAs can process "Downgraded-" header fields. The easiest way to process "Downgraded-" header fields is to remove "Downgraded-" from the decoded "Downgraded-" header fields' name. Then, the "address header fields" may be displayed twice, one is from downgraded header field and the other is from decoded "Downgraded-" header field. Although it is very easy, it MUST NOT be used because of the following reasons. o [RFC5322] section 3.6 defines number of times each field may occur in the header section of a message and the maximum number for "From", "Sender", "To", "Cc", "Bcc" header fields is 1. It violates [RFC5322]. o Users cannot distinguish which is the original downgraded header field and which is the generated header field. o The Downgraded-* header field and corresponding header field may not have relations. The following way is to remove "Downgraded-" from the decoded "Downgraded-" header fields' name and remove the corresponding header field at the same time. 4. Displaying downgraded message MUAs may decode and re-generate the original header fields of the message. This procedure may reconstruct the original message from the downgraded message. But it is not guaranteed. Displaying downgraded message is implemented by the following steps. Step 1: Select Address header field preservation headers described in Section 3.2 of [I-D.ietf-eai-downgrade]. Target header fields are "Downgraded-From", "Downgraded-Sender", "Downgraded-To", "Downgraded-Cc", "Downgraded-Bcc", "Downgraded-Reply-To", "Downgraded-Resent-From", "Downgraded-Resent-Sender", "Downgraded- Resent-To", "Downgraded-Resent-Cc", "Downgraded-Resent-Bcc", "Downgraded-Resent-Reply-To", "Downgraded-Return-Path" and Fujiwara Expires September 10, 2009 [Page 4] Internet-Draft Displaying Downgraded Messages March 2009 "Downgraded-Disposition-Notification-To" header fields. Step 2: Generate new header field which field name is the original header field name and the field value is the MIME decoded header field value from the output of Step 1. Step 3: Apply Email header fields downgrading defined in section 5 of [I-D.ietf-eai-downgrade] to the output of Step 2 without re- generating "Downgraded-" header fields. Step 4: Compare the output of Step 3 and the original header fields. If the same header fields exist for the output of Step 3 and the original header fields, remove the same header fields from the original header fields. This step outputs the original header fields which is modified by this step 4. Before this comparison, a canonicalization described below is useful. 1. Unfold all header field continuation lines as described in [RFC5322]. 2. Insert a space character before and after separator "," if there is no space character. 3. Insert a space character before and after if there is no space character. 4. Decode each whose charset is 'UTF-8'. 5. Convert all sequences of one or more WSP characters to a single space character. WSP characters here include those before and after a line folding boundary. 6. Delete all WSP characters at the end of each unfolded header field value. 7. Delete any WSP characters remaining before and after the colon separating the header field name from the header field value. The colon separator MUST be retained. Step 5: Decode MIME encoded header fields and MIME body part header fields according to [RFC2047] and [RFC2231]. Step 6: For each "Downgraded-" header field except the address header field preservation headers and the envelope information preservation headers described in [I-D.ietf-eai-downgrade] section 3, generate new header field which field name is the original header field name and the field value is the decoded header field value, then replace the original "Downgraded-" header field by the generated header field. Don't change "Downgraded-Mail-From" and "Downgraded-Rcpt-To" header fields because they do not have their original header fields. Don't change the address header field preservation header if it doesn't have the corresponding downgraded header field. Fujiwara Expires September 10, 2009 [Page 5] Internet-Draft Displaying Downgraded Messages March 2009 5. Security considerations While displaying downgraded message changes the header fields of the message and it may lose the original information, MUAs should have a function to read the original received message (with/without MIME decoding). While information in any email header should usually treated with some suspicion, current email systems commonly employ various mechanisms and protocols to make the information more trustworthy. For example, an organization's boundary MTA can modify From: lines so that messages arriving from outside the organization are easily distinguishable from internal emails. As a result of rewriting, the Downgraded-From header field may not be decoded. See "Security considerations" section in [I-D.ietf-eai-downgrade] and [RFC4952] for more discussion. 6. IANA Considerations 7. Acknowledgements 8. Change History This section is used for tracking the update of this document. Will be removed after finalize. 8.1. draft-fujiwara-eai-downgraded-display: Version 00 o Initial version o It is separated from Appendix A of draft-ietf-eai-downgrade-05.txt 8.2. draft-ietf-eai-downgraded-display: Version 00 o Submitted as a working group draft 8.3. draft-ietf-eai-downgraded-display: Version 01 o Prohibited and removed Displaying Technique 1 o Added new texts to Security Considerations 9. Normative References [I-D.ietf-eai-downgrade] Fujiwara Expires September 10, 2009 [Page 6] Internet-Draft Displaying Downgraded Messages March 2009 Fujiwara, K. and Y. Yoneya, "Downgrading mechanism for Email Address Internationalization", draft-ietf-eai-downgrade-12 (work in progress), March 2009. [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. [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", RFC 4952, July 2007. [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, October 2008. [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, October 2008. [RFC5335] Abel, Y., "Internationalized Email Headers", RFC 5335, September 2008. [RFC5336] Yao, J. and W. Mao, "SMTP Extension for Internationalized Email Addresses", RFC 5336, September 2008. [RFC5337] Newman, C. and A. Melnikov, "Internationalized Delivery Status and Disposition Notifications", RFC 5337, September 2008. Appendix A. Examples This section shows a example of displaying downgraded message. Fujiwara Expires September 10, 2009 [Page 7] Internet-Draft Displaying Downgraded Messages March 2009 First, an example of the original UTF8SMTP message and its downgraded message are shown. They are the same as "Example 1" of [I-D.ietf-eai-downgrade]. The example UTF8SMTP message is shown in Figure 1. Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: DISPLAY-local > To: DISPLAY-remote1 > Cc: DISPLAY-remote2 Date: DATE MAIL_BODY Figure 1: Original message Delivered downgraded message is shown in Figure 2. Return-Path header will be added by the final destination MTA. Fujiwara Expires September 10, 2009 [Page 8] Internet-Draft Displaying Downgraded Messages March 2009 Return-Path: Downgraded-Mail-From: =?UTF-8?Q?>?= Downgraded-Rcpt-To: =?UTF-8?Q?>?= Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?= From: =?UTF-8?Q?DISPLAY-local?= Downgraded-From: =?UTF-8?Q?DISPLAY-local_>?= To: =?UTF-8?Q?DISPLAY-remote1?= Downgraded-To: =?UTF-8?Q?DISPLAY-remote1_?= =?UTF-8?Q?>?= Cc: =?UTF-8?Q?DISPLAY-remote2?= Internationalized address =?UTF-8?Q?NON-ASCII-remote2@example.org?= removed:; Downgraded-Cc: =?UTF-8?Q?DISPLAY-remote2_?= =?UTF-8?Q??= Date: DATE MAIL_BODY Figure 2: Downgraded message Figure 3 shows MIME decoded message of Figure 2. The recipient can read the original From, To, Cc header fields as Downgraded-From, Downgraded-To, Downgraded-Cc header fields. Fujiwara Expires September 10, 2009 [Page 9] Internet-Draft Displaying Downgraded Messages March 2009 Return-Path: Downgraded-Mail-From: > Downgraded-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: DISPLAY-local Downgraded-From: DISPLAY-local > To: DISPLAY-remote1 Downgraded-To: DISPLAY-remote1 > Cc: DISPLAY-remote2 Internationalized address NON-ASCII-remote2@example.org removed:; Downgraded-Cc: DISPLAY-remote2 Date: DATE MAIL_BODY Figure 3: MIME decoded message Fujiwara Expires September 10, 2009 [Page 10] Internet-Draft Displaying Downgraded Messages March 2009 A.1. Displaying example This example shows displaying process of 'Displaying technique' for Figure 2. First, perform Step 1. Downgraded-From: =?UTF-8?Q?DISPLAY-local_>?= Downgraded-To: =?UTF-8?Q?DISPLAY-remote1_?= =?UTF-8?Q?>?= Downgraded-Cc: =?UTF-8?Q?DISPLAY-remote2_?= =?UTF-8?Q??= Figure 4: Displaying: Output of Step 1 Then, perform Step 2. From: DISPLAY-local > To: DISPLAY-remote1 > Cc: DISPLAY-remote2 Figure 5: Displaying: Output of Step 2 Perform Step 3. From: =?UTF-8?Q?DISPLAY-local?= To: =?UTF-8?Q?DISPLAY-remote1?= Cc: =?UTF-8?Q?DISPLAY-remote2?= Internationalized address =?UTF-8?Q?NON-ASCII-remote2@example.org?= removed:; Figure 6: Displaying: Output of Step 3 Perform Step 4. "From", "To", "Cc" header fields are removed in Figure 7. Fujiwara Expires September 10, 2009 [Page 11] Internet-Draft Displaying Downgraded Messages March 2009 Return-Path: Downgraded-Mail-From: =?UTF-8?Q?>?= Downgraded-Rcpt-To: =?UTF-8?Q?>?= Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?= Downgraded-From: =?UTF-8?Q?DISPLAY-local_>?= Downgraded-To: =?UTF-8?Q?DISPLAY-remote1?_?= =?UTF-8?Q?>?= Downgraded-Cc: =?UTF-8?Q?DISPLAY-remote2_?= =?UTF-8?Q??= Date: DATE MAIL_BODY Figure 7: Displaying: Output of Step 4 Perform Step 5 and 6. Return-Path: Downgraded-Mail-From: > Downgraded-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: DISPLAY-local > To: DISPLAY-remote1 > Cc: DISPLAY-remote2 Date: DATE MAIL_BODY Figure 8: Decoded message Fujiwara Expires September 10, 2009 [Page 12] Internet-Draft Displaying Downgraded Messages March 2009 As a result, in this simple example, all original header fields are displayed in the original form. Differences between Figure 1 and Figure 8 are Return-Path, Downgraded-Mail-From, Downgraded-Rcpt-To header fields only. Author's Address Kazunori Fujiwara Japan Registry Services Co., Ltd. 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 Fujiwara Expires September 10, 2009 [Page 13]