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
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Abstract
This document describes how to display downgraded messages which
originally contain internationalized E-mail addresses or
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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
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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 <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].
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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
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"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 <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: 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.
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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]
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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.
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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.
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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.
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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
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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_<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.
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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
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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
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