Displaying Downgraded Messages for Email Address Internationalization
draft-ietf-eai-downgraded-display-00.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 April 20, 2009.

Abstract

This document describes how to display downgraded messages which originally contain internationalized E-mail addresses or internationalized header fields.

Table of Contents

1.  Introduction
2.  Terminology
3.  Displaying downgraded message
    3.1.  Displaying technique 1
    3.2.  Displaying technique 2
4.  Security considerations
5.  IANA Considerations
6.  Acknowledgements
7.  Change History
    7.1.  draft-fujiwara-eai-downgraded-display: Version 00
    7.2.  draft-ietf-eai-downgraded-display: Version 00
8.  Normative References
Appendix A.  Examples
    A.1.  Displaying technique 1 example
    A.2.  Displaying technique 2 example
§  Author's Address
§  Intellectual Property and Copyright Statements

1.  Introduction

The Email Address Internationalization (UTF8SMTP) extension document set [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.) [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.) [RFC5337] (Newman, C. and A. Melnikov, “Internationalized Delivery Status and Disposition Notifications,” September 2008.) expands Email address structure, syntax and Email header format. To avoid bouncing internationalized Email messages, the downgrading mechanism [I‑D.ietf‑eai‑downgrade] (Fujiwara, K. and Y. Yoneya, “Downgrading mechanism for Email Address Internationalization,” September 2008.) 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] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) 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 techniques in MUAs.

This is an informational document and it does not supersede the referenced documents.

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

Specialized terms used in this specification are defined in the EAI overview [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) or in [RFC5321] (Klensin, J., “Simple Mail Transfer Protocol,” October 2008.)[RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.), MIME documents [RFC2045] (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) [RFC2183] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.) [RFC2231] (Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” November 1997.).

This document depends on [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.) and [I‑D.ietf‑eai‑downgrade] (Fujiwara, K. and Y. Yoneya, “Downgrading mechanism for Email Address Internationalization,” September 2008.). 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 <mailbox> elements which is defined in [RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.). "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] (Abel, Y., “Internationalized Email Headers,” September 2008.).

3.  Displaying downgraded message

Displaying downgraded message is mostly performed by MIME decoding according to [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) and [RFC2231] (Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” November 1997.). 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. It is described in Section 3.1 (Displaying technique 1) and Section 3.2 (Displaying technique 2).

3.1.  Displaying technique 1

MUAs may remove "Downgraded-" from decoded "Downgraded-" header fields' name.

First, decode MIME encoded header fields and MIME body part header fields according to [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) and [RFC2231] (Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” November 1997.).

Then, for each "Downgraded-" header field, generate new header field which field name is the original header field name and the field value is the decoded header field value, and replace the "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.

With this technique, the "address header fields" may be displayed twice, one is from downgraded header field and the other is from decoded "Downgraded-" header.

3.2.  Displaying technique 2

MUAs may decode and re-generate the original header of the message. This technique may reconstruct the original message from the downgraded message. But it is not guaranteed.

This technique is implemented by the following steps.

Step 1:

Select "Downgraded-" header fields whose original header field is an "address header field". Target header fields are "Downgraded-From", "Downgraded-Sender", "Downgraded-Reply-To", "Downgraded-To", "Downgraded-Cc", "Downgraded-Bcc", "Downgraded-Resent-From", "Downgraded-Resent-Sender", "Downgraded-Resent-To", "Downgraded-Resent-Cc", and "Downgraded-Return-Path" header fields.

Step 2:

Generate new header field which field name is the original header field name and the field value is the 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] (Fujiwara, K. and Y. Yoneya, “Downgrading mechanism for Email Address Internationalization,” September 2008.) 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 both the output 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. Before this comparison, a canonicalization described below is useful.

1. Unfold all header field continuation lines as described in [RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.).
2. Insert a space character before and after <mailbox-list> separator "," if there is no space character.
3. Insert a space character before and after <comment> if there is no space character.
4. Decode <encoded-word> 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:

Finally, do 'Displaying technique 1' described in Section 3.1 (Displaying technique 1) to the output of Step 4.

4.  Security considerations

Displaying downgraded message may break the header of the message. MUAs should have a function to read the original received message.

See "Security considerations" section in [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) for more discussion.

5.  IANA Considerations

6.  Acknowledgements

7.  Change History

This section is used for tracking the update of this document. Will be removed after finalize.

7.1.  draft-fujiwara-eai-downgraded-display: Version 00

• Initial version
• It is separated from Appendix A of draft-ietf-eai-downgrade-05.txt

7.2.  draft-ietf-eai-downgraded-display: Version 00

• Submitted as a working group draft

8. Normative References

Appendix A.  Examples

This section shows a example of displaying downgraded message. 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] (Fujiwara, K. and Y. Yoneya, “Downgrading mechanism for Email Address Internationalization,” September 2008.). The example UTF8SMTP message is shown in Figure 1 (Original message).

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 <NON-ASCII-local@example.com
 <ASCII-local@example.com>>
To: DISPLAY-remote1 <NON-ASCII-remote1@example.net
 <ASCII-remote1@example.net>>
Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org>
Date: DATE

MAIL_BODY

Delivered downgraded message is shown in Figure 2 (Downgraded message). Return-Path header will be added by the final destination MTA.

Return-Path: <ASCII-local@example.com>
Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com>_?=
 =?UTF-8?Q?<ASCII-local@example.com>?=
Downgraded-Rcpt-To: =?UTF-8?Q?<NON-ASCII-remote1@example.net>_?=
 =?UTF-8?Q?<ASCII-remote1@example.net>?=
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?= <ASCII-local@example.com>
Downgraded-From: =?UTF-8?Q?DISPLAY-local_<NON-ASCII-local@example.com_?=
 =?UTF-8?Q?<ASCII-local@example.com>>?=
To: =?UTF-8?Q?DISPLAY-remote1?= <ASCII-remote1@example.net>
Downgraded-To: =?UTF-8?Q?DISPLAY-remote1_?=
 =?UTF-8?Q?<NON-ASCII-remote1@example.net_<ASCII-remote1@example.net>>?=
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?<NON-ASCII-remote2@example.org>?=
Date: DATE

MAIL_BODY

Figure 3 (MIME decoded message) shows MIME decoded message of Figure 2 (Downgraded message). The recipient can read the original From, To, Cc header fields as Downgraded-From, Downgraded-To, Downgraded-Cc header fields.

Return-Path: <ASCII-local@example.com>
Downgraded-Mail-From: <NON-ASCII-local@example.com>
 <ASCII-local@example.com>
Downgraded-Rcpt-To: <NON-ASCII-remote1@example.net>
 <ASCII-remote1@example.net>
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 <ASCII-local@example.com>
Downgraded-From: DISPLAY-local <NON-ASCII-local@example.com
 <ASCII-local@example.com>>
To: DISPLAY-remote1 <ASCII-remote1@example.net>
Downgraded-To: DISPLAY-remote1 <NON-ASCII-remote1@example.net
 <ASCII-remote1@example.net>>
Cc: DISPLAY-remote2 Internationalized address
 NON-ASCII-remote2@example.org removed:;
Downgraded-Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org>
Date: DATE

MAIL_BODY

A.1.  Displaying technique 1 example

After removing "Downgraded-" from decoded "Downgraded-" header fields from Figure 3 (MIME decoded message), 'Displaying technique 1' example is shown in Figure 4 (Displaying technique 1).

Return-Path: <ASCII-local@example.com>
Mail-From: <NON-ASCII-local@example.com>
 <ASCII-local@example.com>
Rcpt-To: <NON-ASCII-remote1@example.net>
 <ASCII-remote1@example.net>
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 <ASCII-local@example.com>
From: DISPLAY-local <NON-ASCII-local@example.com
 <ASCII-local@example.com>>
To: DISPLAY-remote1 <ASCII-remote1@example.net>
To: DISPLAY-remote1 <NON-ASCII-remote1@example.net
 <ASCII-remote1@example.net>>
Cc: DISPLAY-remote2 Internationalized address
 NON-ASCII-remote2@example.org removed:;
Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org>
Date: DATE

MAIL_BODY

A.2.  Displaying technique 2 example

This example shows displaying process of 'Displaying technique 2' for Figure 2 (Downgraded message).

First, perform Step 1.

Downgraded-From: =?UTF-8?Q?DISPLAY-local_<NON-ASCII-local@example.com_?=
 =?UTF-8?Q?<ASCII-local@example.com>>?=
Downgraded-To: =?UTF-8?Q?DISPLAY-remote1_?=
 =?UTF-8?Q?<NON-ASCII-remote1@example.net_<ASCII-remote1@example.net>>?=
Downgraded-Cc: =?UTF-8?Q?DISPLAY-remote2_?=
 =?UTF-8?Q?<NON-ASCII-remote2@example.org>?=

Then, perform Step 2.

From: DISPLAY-local <NON-ASCII-local@example.com
 <ASCII-local@example.com>>
To: DISPLAY-remote1 <NON-ASCII-remote1@example.net
 <ASCII-remote1@example.net>>
Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org>

Perform Step 3.

From: =?UTF-8?Q?DISPLAY-local?= <ASCII-local@example.com>
To: =?UTF-8?Q?DISPLAY-remote1?= <ASCII-remote1@example.net>
Cc: =?UTF-8?Q?DISPLAY-remote2?= Internationalized address
 =?UTF-8?Q?NON-ASCII-remote2@example.org?= removed:;

Perform Step 4. "From", "To", "Cc" header fields are removed in Figure 8 (Displaying technique 2: Output of Step 4).

Return-Path: <ASCII-local@example.com>
Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com>?=
 =?UTF-8?Q?<ASCII-local@example.com>?=
Downgraded-Rcpt-To: =?UTF-8?Q?<NON-ASCII-remote1@example.net>_?=
 =?UTF-8?Q?<ASCII-remote1@example.net>?=
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_<NON-ASCII-local@example.com_?=
 =?UTF-8?Q?<ASCII-local@example.com>>?=
Downgraded-To: =?UTF-8?Q?DISPLAY-remote1?_?=
 =?UTF-8?Q?<NON-ASCII-remote1@example.net_<ASCII-remote1@example.net>>?=
Downgraded-Cc: =?UTF-8?Q?DISPLAY-remote2_?=
 =?UTF-8?Q?<NON-ASCII-remote2@example.org>?=
Date: DATE

MAIL_BODY

Perform Step 5. (Apply 'Displaying technique 1'.)

Return-Path: <ASCII-local@example.com>
Downgraded-Mail-From: <NON-ASCII-local@example.com>
 <ASCII-local@example.com>
Downgraded-Rcpt-To: <NON-ASCII-remote1@example.net>
 <ASCII-remote1@example.net>
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 <NON-ASCII-local@example.com
 <ASCII-local@example.com>>
To: DISPLAY-remote1 <NON-ASCII-remote1@example.net
 <ASCII-remote1@example.net>>
Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org>
Date: DATE

MAIL_BODY

As a result, in this simple example, all original header fields are displayed in the original form. Differences between Figure 1 (Original message) and Figure 9 (Display technique 2: Decoded message) are Return-Path, Downgraded-Mail-From, Downgraded-Rcpt-To header fields only.

Author's Address

Full Copyright Statement

Copyright © 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.