Email Address Internationalization                           K. Fujiwara
(EAI)                                                               JPRS

Intended status: Experimental
Expires: April 20, September 10, 2009

 Displaying Downgraded Messages for Email Address Internationalization
                draft-ietf-eai-downgraded-display-00.txt
                draft-ietf-eai-downgraded-display-01.txt

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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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Displaying  Consideration of displaying downgraded message . . . . . . . . . . . . . . . .  4
     3.1.  Displaying technique 1 . . . . . . . . . . . . . . . . . .  4
     3.2.
   4.  Displaying technique 2 . . downgraded message  . . . . . . . . . . . . . . . .  4
   4.
   5.  Security considerations  . . . . . . . . . . . . . . . . . . .  5
   5.  6
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   6.
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  6
   7.
   8.  Change History . . . . . . . . . . . . . . . . . . . . . . . .  6
     7.1.
     8.1.  draft-fujiwara-eai-downgraded-display: Version 00  . . . .  6
     7.2.
     8.2.  draft-ietf-eai-downgraded-display: Version 00  . . . . . .  6
   8.
     8.3.  draft-ietf-eai-downgraded-display: Version 01  . . . . . .  6
   9.  Normative References . . . . . . . . . . . . . . . . . . . . .  6
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . .  7
     A.1.  Displaying technique 1 example . . . . . . . . . . . . . . 10
     A.2.  Displaying technique 2 example . . . . . . . . . . . . . . 10 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 14

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
   techniques
   downgraded messages 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].

   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 <mailbox> 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].

3.  Displaying  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.  It

   The easiest way to process "Downgraded-" header fields is
   described in Section 3.1 and Section 3.2.

3.1.  Displaying technique 1

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

   First, decode MIME encoded header fields and MIME body part header
   fields according to [RFC2047] and [RFC2231].
   Then, for each "Downgraded-" header field, generate new the "address header field
   which field name fields" may be displayed twice, one is the original from
   downgraded header field name and the field
   value other is the from decoded "Downgraded-"
   header field value, and replace field.  Although it is very easy, it MUST NOT be used because
   of the
   "Downgraded-" header following reasons.
   o  [RFC5322] section 3.6 defines number of times each field by may occur
      in the generated header field.

   Don't change "Downgraded-Mail-From" section of a message and "Downgraded-Rcpt-To" the maximum number for
      "From", "Sender", "To", "Cc", "Bcc" header fields because they do not have their is 1.  It
      violates [RFC5322].
   o  Users cannot distinguish which is the original downgraded header fields.

   With this technique,
      field and which is the "address generated header fields" may be displayed
   twice, one is from downgraded field.
   o  The Downgraded-* header field and the other corresponding header field may
      not have relations.

   The following way is to remove "Downgraded-" from the decoded
   "Downgraded-" header.

3.2. header fields' name and remove the corresponding header
   field at the same time.

4.  Displaying technique 2 downgraded message

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

   This technique

   Displaying downgraded message is implemented by the following steps.

   Step 1:   Select "Downgraded-" header fields whose original Address header field is an "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-Reply-To", "Downgraded-To",
      "Downgraded-Cc", "Downgraded-Bcc", "Downgraded-
      Resent-From", "Downgraded-Reply-To",
      "Downgraded-Resent-From", "Downgraded-Resent-Sender", "Downgraded-Resent-To", "Downgraded-
      Resent-To", "Downgraded-Resent-Cc", and "Downgraded-Resent-Bcc",
      "Downgraded-Resent-Reply-To", "Downgraded-Return-Path" and
      "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 both 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. 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 <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 each <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'   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
      Section 3.1 to [I-D.ietf-eai-downgrade] section
      3, generate new header field which field name is the output of Step 4.

4. 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.

5.  Security considerations

   Displaying

   While displaying downgraded message may break changes the header fields of the message.
   message and it may lose the original information, MUAs should have a
   function to read the original received message. 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.

5.

6.  IANA Considerations

6.  Acknowledgements

7.  Acknowledgements

8.  Change History

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

7.1.

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

7.2.

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

   o  Submitted as a working group draft

8.

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, K. and Y. Yoneya, "Downgrading mechanism for
              Email Address Internationalization",
              draft-ietf-eai-downgrade-09
              draft-ietf-eai-downgrade-12 (work in progress),
              September 2008.
              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.

   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 <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

                        Figure 1: Original message

   Delivered downgraded message is shown in Figure 2.  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>?= =?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>?= =?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 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.

   Return-Path: <ASCII-local@example.com>
   Downgraded-Mail-From: <NON-ASCII-local@example.com>
    <ASCII-local@example.com> <NON-ASCII-local@example.com
    <ASCII-local@example.com>>
   Downgraded-Rcpt-To: <NON-ASCII-remote1@example.net>
    <ASCII-remote1@example.net> <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

                      Figure 3: MIME decoded message

A.1.  Displaying technique 1 example

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

   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

                     Figure 4: Displaying technique 1

A.2.  Displaying technique 2 example

   This example shows displaying process of 'Displaying technique 2' technique' for
   Figure 2.

   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>?=

                  Figure 5: Displaying technique 2: 4: Displaying: Output of Step 1

   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>

                  Figure 6: Displaying technique 2: 5: Displaying: Output of Step 2

   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:;

                  Figure 7: Displaying technique 2: 6: Displaying: Output of Step 3

   Perform Step 4.  "From", "To", "Cc" header fields are removed in
   Figure 8. 7.

Return-Path: <ASCII-local@example.com>
Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com>?=
 =?UTF-8?Q?<ASCII-local@example.com>?= =?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>?= =?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

                  Figure 8: Displaying technique 2: 7: Displaying: Output of Step 4

   Perform Step 5.  (Apply 'Displaying technique 1'.) 5 and 6.

   Return-Path: <ASCII-local@example.com>
   Downgraded-Mail-From: <NON-ASCII-local@example.com>
    <ASCII-local@example.com> <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

                         Figure 9: Display technique 2: 8: Decoded message
   As a result, in this simple example, all original header fields are
   displayed in the original form.  Differences between Figure 1 and
   Figure 9 8 are Return-Path, Downgraded-Mail-From, Downgraded-Rcpt-To
   header fields only.

Author's Address

   Kazunori Fujiwara
   JPRS
   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

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   ietf-ipr@ietf.org.