Email Address Internationalization                           K. Fujiwara
(EAI)                                                               JPRS

Intended status: Experimental
Expires: September 10, 2009 March 12, 2010

 Displaying Downgraded Messages for Email Address Internationalization
                draft-ietf-eai-downgraded-display-01.txt
                draft-ietf-eai-downgraded-display-02.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on September 10, 2009. March 12, 2010.

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   This document describes how to display a method for displaying downgraded messages
   which originally contain contained internationalized E-mail addresses or
   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
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  6  7
   8.  Change History . . . . . . . . . . . . . . . . . . . . . . . .  6  7
     8.1.  draft-fujiwara-eai-downgraded-display: Version 00  . . . .  6  7
     8.2.  draft-ietf-eai-downgraded-display: Version 00  . . . . . .  6  7
     8.3.  draft-ietf-eai-downgraded-display: Version 01  . . . . . .  6  7
     8.4.  draft-ietf-eai-downgraded-display: Version 02  . . . . . .  7
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     9.2.  Informative References . .  6 . . . . . . . . . . . . . . . .  8
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . .  7  9
     A.1.  Displaying example . . . . . . . . . . . . . . . . . . . . 11 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 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 rejection of
   internationalized Email messages, the downgrading mechanism
   [I-D.ietf-eai-downgrade] [RFC5504]
   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]. [RFC5504].  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.  Consideration of displaying downgraded message

   Displaying downgraded message is mostly performed by MIME decoding
   according to [RFC2047] and [RFC2231].  Result  As a result of MIME decoding,
   the header of the message still contains Downgraded-*: "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 A MUA can process "Downgraded-" header fields.

   The easiest way to process "Downgraded-" header fields is to remove
   "Downgraded-" from the decoded "Downgraded-" header fields' name. names.
   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-* "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

   A MUA MAY decode and re-generate the original header fields of the
   message.  This procedure may reconstruct the original message from can be used to reverse the downgraded message.  But it is Downgrade process
   but will not guaranteed. construct exactly the original header fields in all
   cases.

   Displaying downgraded message is implemented by the following steps.

   Input:
      The input to this procedure is the header of the message as
      received.  Copy the entire header into an edit space.

   Step 1:
      Select Address header field preservation headers the "Address Header Fields' Preservation Header Fields"
      described in Section 3.2 of [I-D.ietf-eai-downgrade].  Target [RFC5504] in the edit space.  These
      header fields are "Downgraded-From", "Downgraded-Sender",
      "Downgraded-To", "Downgraded-Cc", "Downgraded-Bcc", "Downgraded-Reply-To", "Downgraded-
      Reply-To", "Downgraded-Resent-From", "Downgraded-Resent-Sender", "Downgraded-
      Resent-To",
      "Downgraded-Resent-To", "Downgraded-Resent-Cc", "Downgraded-Resent-Bcc", "Downgraded-
      Resent-Bcc", "Downgraded-Resent-Reply-To", "Downgraded-Return-Path" "Downgraded-Return-
      Path" and "Downgraded-Disposition-Notification-To" header fields.

   Step 2:   Generate
      For each header field from the output of Step 1, generate a new
      header field which where the field name is the original header field
      name and the field value is the result of MIME decoded decoding header
      field value from the output of Step 1. value.

   Step 3:
      Apply Email header fields downgrading "Email Header Fields Downgrading" defined in section 5 of [I-D.ietf-eai-downgrade]
      [RFC5504] to the output of Step 2 without re-
      generating re-generating
      "Downgraded-" header fields.

   Step 4:   Compare fields and copy the output of into a new space
      (hereafter, call it as a "comparison space").

   Step 3 and the original header
      fields.  If 4:
      Compare the same header fields exist for the output of Step 3
      and in the original header fields, remove comparison space with the same header
      fields from of the original header fields.  This step outputs same name in the original header
      fields which is modified by this step 4. edit space.  Before this
      comparison,
      a canonicalization canonicalize each header field described below is useful. below.

      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.

      For each header field, if the same header fields exist in the
      comparison space and in the edit space, remove the original header
      field in the edit space and the generated header field in the
      comparison space.

      Remaining header fields in the comparison space may be bogus or
      broken "Address Header Fields' Preservation Header Fields" origin.

   Step 5:
      Decode all MIME encoded header fields and MIME body part header
      fields according to [RFC2047] and [RFC2231].
      [RFC2231] in the edit space.

   Step 6:
      For each "Downgraded-" header field except the address
      header field preservation headers and the envelope information
      preservation headers "Unknown Header Fields' Preservation Header Fields"
      described in [I-D.ietf-eai-downgrade] section
      3, 3.3 of [RFC5504] and "Address Header Fields'
      Preservation Header Fields", generate a new header field which where the
      field name is the original header field name and the field value
      is the decoded result of MIME decoding 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

   While displaying downgraded message changes in the header fields edit space.  "Envelope Information Preservation
      Header Fields" are not targets of this step.

   The output of this procedure is an UTF8SMTP header in the
   message and it may lose edit space.
   It will closely resemble the original information, MUAs should have a
   function to read header.

   After this procedure, the original received message (with/without MUA may decode MIME
   decoding). body part header fields
   according to [RFC2047] and [RFC2231].

5.  Security considerations

   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: "From:" lines
   so that messages arriving from outside the organization are easily
   distinguishable from internal emails.  As a result of rewriting, the
   Downgraded-From
   "Downgraded-From" header field may not be decoded.

   A MUA may emphasize bogus or broken "Downgraded-" header fields in
   step 4 of Section 4.

   Hiding the information from the actual header fields when using the
   "Downgraded-" header fields does not cause loss of information if the
   comparison done in step 4 of Section 4 is successful.  To ensure that
   no information is lost, a MUA SHOULD have a function that uses the
   actual message that was received (with/without MIME decoding) to
   render the message.

   See "Security considerations" section in [I-D.ietf-eai-downgrade] [RFC5504] and [RFC4952] for
   more discussion.

6.  IANA Considerations

   This document makes no requests for IANA action.  This section can be
   removed by the RFC Editor before publication.

7.  Acknowledgements

   This document was separated from [RFC5504].  Both documents were
   developed in the EAI WG.  Significant comments and suggestions were
   received from John Klensin, Harald Alvestrand, Chris Newman, Randall
   Gellens, Charles Lindsey, Marcos Sanz, Alexey Melnikov, Frank
   Ellermann, Edward Lewis, S. Moonesamy and JET members.

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

8.4.  draft-ietf-eai-downgraded-display: Version 02

   o  updated by comments from Chair's review and AD's review
   o  Fixed references
   o  Rewrote section 4 to be more comprehensible
   o  Added bogus or broken "Downgraded-" header fields
   o  Added sentences in Security considerations

9.  References

9.1.  Normative References

   [I-D.ietf-eai-downgrade]
              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.

   [RFC5504]  Fujiwara, K. and Y. Yoneya, "Downgrading Mechanism for
              Email Address Internationalization", RFC 5504, March 2009.

9.2.  Informative References

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 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]. [RFC5504].
   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>>?=
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 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>>
   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

                      Figure 3: MIME decoded message

A.1.  Displaying example

   This example shows displaying process processes of 'Displaying technique' downgraded message' 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 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 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 6: Displaying: Output of Step 3

   Perform Step 4.  "From", "To", "Cc" header fields are removed in
   Figure 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>>?=
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

                  Figure 7: Displaying: Output of Step 4

   Perform Step 5 and 6.

   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

                         Figure 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 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 +81-3-5215-8451
   Email: fujiwara@jprs.co.jp