Email Address Internationalization Y. YONEYA, Ed.
(EAI) K. Fujiwara, Ed.
Internet-Draft JPRS
Intended status: Experimental July 6, 2007
Expires: January 7, 2008
Downgrading mechanism for Email Address Internationalization
draft-ietf-eai-downgrade-04.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Traditional mail systems handle only US-ASCII characters in SMTP
envelope and mail header fields. The Email Address
Internationalization (UTF8SMTP) allows UTF-8 characters in SMTP
envelope and mail header fields. To deliver internationalized Email
messages to/via UTF8SMTP non-compliant environment, some sort of
converting mechanism is required. This document describes
downgrading mechanism for Email Address Internationalization.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. New header fields definition . . . . . . . . . . . . . . . . . 4
4. SMTP Downgrading . . . . . . . . . . . . . . . . . . . . . . . 5
5. Email header fields downgrading . . . . . . . . . . . . . . . 6
6. MIME body part headers downgrading . . . . . . . . . . . . . . 9
7. Security considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. Change History . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. draft-yoneya-ima-downgrade: Version 00 . . . . . . . . . 11
10.2. draft-yoneya-ima-downgrade: Version 01 . . . . . . . . . 11
10.3. draft-ietf-eai-downgrade: Version 00 . . . . . . . . . . 11
10.4. draft-ietf-eai-downgrade: Version 01 . . . . . . . . . . 12
10.5. draft-ietf-eai-downgrade: Version 02 . . . . . . . . . . 12
10.6. draft-ietf-eai-downgrade: Version 03 . . . . . . . . . . 12
10.7. draft-ietf-eai-downgrade: Version 04 . . . . . . . . . . 12
11. Normative References . . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Displaying downgraded message . . . . . . . . . . . . 14
A.1. Displaying technique 1 . . . . . . . . . . . . . . . . . 14
A.2. Displaying technique 2 . . . . . . . . . . . . . . . . . 14
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 14
B.1. Downgrading example 1 . . . . . . . . . . . . . . . . . . 14
B.2. Displaying example (Displaying technique 1) . . . . . . . 17
B.3. Displaying example (Displaying technique 2) . . . . . . . 17
B.4. Downgrading example 2 . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 22
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1. Introduction
Traditional mail systems which are defined by [RFC2821] and [RFC2822]
allow US-ASCII characters in SMTP envelope and mail header field
values. The UTF8SMTP proposals [I-D.ietf-eai-framework],
[I-D.ietf-eai-utf8headers] and [I-D.ietf-eai-smtpext] allow UTF-8
characters in SMTP envelope and mail header field values.
Delivering non-ASCII mail addresses from a sender to recipients
requires all components on the mail delivery route are UTF8SMTP
compliant. Otherwise, non-ASCII mail address can't be delivered. To
solve the problem, this document describes downgrading mechanism that
enables delivering non-ASCII mail addresses to traditional mail
system by converting them to corresponding US-ASCII representation.
And more, [I-D.ietf-eai-utf8headers] expands that mail header fields
and MIME header fields are allowed to use any UTF-8 characters. This
downgrading mechanism targets mail header fields and MIME header
fields to be converted to US-ASCII only to send to UTF8SMTP non-
compliant receivers.
[I-D.ietf-eai-smtpext] section 2.2 defines when downgrading occurs.
Mail clients (MUAs, MSAs, MTAs) try to deliver Email messages to SMTP
servers by static setting or DNS MX resource records resolution. If
the SMTP client has an UTF8SMTP envelope or an UTF8SMTP message and
the SMTP client detects that SMTP server doesn't support "UTF8SMTP"
option at EHLO, then the SMTP client MUST NOT send the UTF8SMTP
envelope or UTF8SMTP message to the SMTP server. The section shows 4
choices. The second choice "reject or generate a notification of
non-deliverability" is always allowed. The fourth choice is
downgrading.
Downgrading may be implemented in MUAs, MSAs, MTAs, MDAs which
generates or receives UTF8SMTP envelopes or UTF8SMTP messages and may
send them to non-UTF8SMTP compliant systems.
This document tries to define the downgrading process clearly and it
preserves the original information as much as possible.
Downgrading in UTF8SMTP consists of the following four parts:
o New header fields definition
o SMTP downgrading
o Email header fields downgrading
o MIME header fields downgrading
Before sending to traditional SMTP server, the downgrading process
need to perform SMTP downgrading, Email header fields downgrading,
and MIME header fields downgrading.
In Section 3, two header fields are introduced. One is "Envelope-
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Downgraded:", it preserves the original envelope information. The
other is "Downgraded:", it preserves the original header fields which
contains non-ASCII email addresses or which does not have clear
downgrading definition.
The SMTP downgradin is described in Section 4. It generates US-ASCII
only envelope information from an UTF8SMTP envelope.
The Email header fields downgrading is described in Section 5. It
generates US-ASCII only header fields.
The MIME header fields are expanded in [I-D.ietf-eai-utf8headers].
The MIME header fields downgrading is described in Section 6. It
generates US-ASCII only MIME header fields.
2. Terminology
The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
and "MAY" in this document are to be interpreted as described in RFC
2119 [RFC2119].
All specialized terms used in this specification are defined in the
EAI overview [I-D.ietf-eai-framework] or in [RFC2821][RFC2822], MIME
documents [RFC2045] [RFC2047] [RFC2183] [RFC2231]. The terms "ASCII
address", "internationalized email address", "non-ASCII address",
"i18mail address", "UTF8SMTP", "message" and "mailing list" are used
with the definitions from [I-D.ietf-eai-framework] document.
This document depends on [I-D.ietf-eai-smtpext],
[I-D.ietf-eai-utf8headers], and [I-D.ietf-eai-dsn]. 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.
An "UTF8SMTP envelope" has Email originator/recipient addresses
expanded by [I-D.ietf-eai-smtpext] and [I-D.ietf-eai-dsn].
An "UTF8SMTP message" is Email messages expanded by
[I-D.ietf-eai-utf8headers].
3. New header fields definition
A generic encapsulation header "Downgraded:" is defined to preserve
the original header field. It has two value fields. The former
value field holds the original header field name. The latter value
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field holds the original header field value. Any original header
field value is treated as an unstructured value. The latter value
field of this header MUST be encoded by [RFC2047] section 5(1) method
with charset='UTF-8' same as a 'Subject' header. The header field
syntax is specified as follows:
fields =/ downgraded
downgraded = "Downgraded:" [FWS] field-name ":" unstructured CRLF
Encapsulating a header in a Downgraded: header is defined as:
1. Generate new Downgraded: header whose former value is the
original header field name and latter value is the original
header fleid value.
2. Encode the generated header by [RFC2047] section 5(1) method with
charset='UTF-8'.
3. Replace the original header field as the generated header field.
Another new header "Envelope-Downgraded:" is defined to preserve SMTP
envelope downgraded information. SMTP envelope downgraded
information consists of the original non-ASCII address and the
downgraded all-ASCII address. The non-ASCII address is encoded by
[RFC2047] with charset='UTF-8'. The header field syntax is specified
as follows:
fields =/ edowngraded
edowngraded = "Envelope-Downgraded:" [FWS] edowngraded-field ":"
[FWS] "<" uPath ">" [FWS]
"<" Mailbox ">" [FWS] CRLF
edowngraded-field = "From" / "To"
Original non-ASCII address <uPath> is defined in
[I-D.ietf-eai-smtpext]. <Mailbox> is defined in [RFC2821], section
4.1.2. The "Envelope-Downgraded:" header field is encoded by
[RFC2047] in the downgraded message.
4. SMTP Downgrading
Target of downgrading elements in SMTP envelope are below:
o MAIL FROM:
o RCPT TO:
o ORCPT parameter
Downgrading in SMTP envelope uses ALT-ADDRESS parameter defined in
[I-D.ietf-eai-smtpext]. An address is downgradable if the address is
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US-ASCII address or the address has US-ASCII address specified by
ALT-ADDRESS parameter.
If each recipient address and the return address is downgradable, the
SMTP to the recipient is downgradable.
Even if no downgrading is performed for envelope from/to, MUA/MTA
MUST downgrade message header fields and MIME header fields in the
message body including non-ASCII characters. This is described in
Section 5 and Section 6.
MTA replaces non-ASCII mail address with specified alternative US-
ASCII address when downgrading. Before replacing, decode the ALT-
ADDRESS parameter value because it is encoded as xtest [RFC3461].
Also MTA preserves original information using "Envelope-Downgraded"
header defined in Section 3 with From or To field name. The non-
ASCII mail addresses are encoded by [RFC2047] and put into "Envelope-
Downgraded" header.
Not to disclose whole recipient addresses, MUA/MTA MUST NOT add
"Envelope-Downgraded: To:" header if the SMTP downgrading targets
multiple recipients. See Section 7 for more detail.
While the recipient address downgrading, the "RCPT TO" command may
have an ORCPT parameter. The ORCPT parameter is used for DSN
[RFC3461]. If the ORCPT parameter contains "utf-8" address type
address and the address contains non-ASCII characters, the ORCPT
parameter MUST be converted to utf-8-addr-xtext form or utf-8-addr-
unitext form which is described in [I-D.ietf-eai-dsn].
5. Email header fields downgrading
This section defines conversion method to US-ASCII for each header
field which may contain non-ASCII characters. Header fields are
listed in [RFC4021]. If the whole mail header field does not contain
non-ASCII characters, email header field downgrading is not required.
If the header field contains non-ASCII characters, convert the header
field. Each header field's downgrading method is described below.
o Downgrading Address header fields
From:
Sender:
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Reply-To:
To:
Cc:
Bcc:
Resent-From:
Resent-Sender:
Resent-To:
Resent-Cc:
The header field value is composed of single or multiple <angle-
addr>/<utf8-addr-spec> fields defined in
[I-D.ietf-eai-utf8headers].
If the header has no <angle-addr> or <utf8-addr-spec> which
contains non-ASCII characters, only "display-name" part or
comments contain non-ASCII characters, the "display-name" or
comments are encoded by [RFC2047] with charset='UTF-8'.
Otherwise, preserve the header field in "Downgraded:" header,
generate US-ASCII only address header, and replace the original
header field with the generated US-ASCII only header field. New
header generation method are shown in below.
Extract every field and downgrade each <mailbox>/<angle-addr>/
<utf8-addr-spec>.
If the non-ASCII address is in <utf8-addr-spec> form, then rewrite
it as "Internationalized Address utf8-addr-spec-encoded
Removed:;". "utf8-addr-spec" is encoded to "utf8-addr-spec-
encoded" by [RFC2047].
The field may contain multiple <comment> fields. The <comment>
fields are encoded by [RFC2047] with charset='UTF-8', if
necessary.
<mailbox> is defined as "display-name <angle-addr>" in
[I-D.ietf-eai-utf8headers]. The "display-name" field is encoded
by [RFC2047] with charset='UTF-8', if necessary.
The <angle-addr> may contain comments. Before processing, remove
comments from the <angle-addr>.
UTF8SMTP <angle-addr> defined in [I-D.ietf-eai-utf8headers]
consists of 3 forms. Downgrading method is defined for each form.
* <US-ASCII>
<US-ASCII> is used as is.
* <non-ASCII>
Non-ASCII mail address without sender-specified US-ASCII
address is replaced as
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"Internationalized Address non-ASCII-encoded Removed:;".
non-ASCII address is encoded to "non-ASCII-encoded" by
[RFC2047].
* <non-ASCII <US-ASCII>>
Non-ASCII mail address with sender-specified US-ASCII address
MUST be replaced as "display-name <US-ASCII>".
o Downgrading Non-ASCII in comments
Date:
Message-ID:
In-Reply-To:
References:
Resent-Date:
Resent-Message-ID:
MIME-Version:
Content-ID:
These header fields do not contain non-ASCII characters except in
comments. If the header contains UTF-8 characters in comments,
encode the header by [RFC2047] with charset='UTF-8'.
o Trace header
Received:
If the FOR clause contains non-ASCII addresses, remove the FOR
clause in the header. The other part does not contain non-ASCII
values.
o MIME Content header
Content-Type:
Content-Disposition:
Encode the header by [RFC2231] with charset='UTF-8'.
o Unstructured text headers and structured text headers
Subject:
Comments:
Keywords:
Content-Description:
Encode the header by [RFC2047] with charset='UTF-8'.
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o URI headers
List-Archive:
List-Help:
List-Owner:
List-Post:
List-Subscribe:
List-Unsubscribe:
If the header contains UTF-8 characters in comments, encode the
header by [RFC2047] with charset='UTF-8'. If the header contains
UTF-8 characters in URI, Encode the URI by [RFC3987].
o Other target headers
All other headers which contains non-ASCII characters are
preserved in Downgraded: header and removed.
o ASCII only headers
Content-Transfer-Encoding:
This header is not target of downgrading.
Downgraded header fields should be inserted or replaced at the same
position of the original header field.
6. MIME body part headers downgrading
MIME body part header fields may contain non-ASCII characters
[I-D.ietf-eai-utf8headers]. This section defines conversion method
to US-ASCII for each MIME header field which may contain non-ASCII
characters. Parse the message body's MIME structure for all level
and check all MIME header fields whether contains non-ASCII
characters. If the header contains non-ASCII characters in the
header value, the header is a target of the MIME body part headers
downgrading. Each MIME header field's downgrading method is
described below:
Content-ID:
The Content-ID: header does not contain non-ASCII characters
except in comments. If the header contains UTF-8 characters in
comments, encode the header by [RFC2047] with charset='UTF-8'.
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Content-Type:
Content-Disposition:
Encode the header by [RFC2231] with charset='UTF-8'.
Content-Description:
Encode the header by [RFC2047] with charset='UTF-8'.
Content-Transfer-Encoding:
This header does not contain non-ASCII characters.
7. Security considerations
o Rewriting headers increases the opportunities for undetected
spoofing.
o Recipients addresses can be undisclosed if those addresses are
listed on Bcc or group address. Those undisclosed addresses are
used only in the Envelope. Copying information from the Envelope
into headers creates some risk of inadvertent information
disclosure (not just about addresses).
o It is likely that the techniques suggested here will invalidate
methods that depend on signatures over headers or the envelope.
"Issues" does talk about that, but, because this document strongly
implies that one can downgrade and then upgrade again with no risk
of loss of information, the topic should be explored further.
o Many gateways and servers on the Internet will discard headers
with which they are not familiar. To the extent to which the
downgrade procedures depend on new headers (e.g., "Downgraded") to
avoid information loss, then the risk of having those headers
dropped and its implications must be identified. In particular,
it appears to me that, if the Downgraded headers are dropped,
there is no possibility of reconstructing the original information
at any point (before, during, or after delivery).
See "Security considerations" section in [I-D.ietf-eai-framework] for
more discussion.
8. IANA Considerations
IANA is requested to register the following header fields in the
Permanent Message Header Field Repository, in accordance with the
procedures set out in [RFC3864].
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Header field name: Downgraded
Applicable protocol: mail
Status: experimental
Author/change controller: IETF
Specification document(s): This document (Section 3)
Header field name: Envelope-Downgraded
Applicable protocol: mail
Status: experimental
Author/change controller: IETF
Specification document(s): This document (Section 3)
9. Acknowledgements
Significant comments and suggestions were received from John Klensin,
Harald Alvestrand, Chris Newman, Charles Lindsey, Marcos Sanz, Alexey
Melnikov, Frank Ellermann and JET members.
10. Change History
This section is used for tracking the update of this document. Will
be removed after finalize.
10.1. draft-yoneya-ima-downgrade: Version 00
o Initial version
o Followed draft-yeh-ima-utf8headers-00 and draft-yao-smtpext-00
10.2. draft-yoneya-ima-downgrade: Version 01
o Document structure was changed
o Followed draft-yeh-ima-utf8headers-01 and draft-yao-smtpext-02
o Downgrading requirements were added
o SMTP DATA encapsulation method was proposed
o Downgrading examples was provided
10.3. draft-ietf-eai-downgrade: Version 00
o Followed draft-yeh-ima-utf8headers-01 and
draft-ietf-eai-smtpext-00
o No header downgrading method was proposed
o Header encapsulation method was proposed
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10.4. draft-ietf-eai-downgrade: Version 01
o Followed draft-ietf-eai-utf8headers-00
o Header conversion and encapsulation method was merged
o Header conversion method was defined in detail
10.5. draft-ietf-eai-downgrade: Version 02
o Followed draft-ietf-eai-utf8headers-01 and
draft-ietf-eai-smtpext-01
o Specification about algorithmic generated address is removed
o No header downgrading method was removed
o SMTP DATA encapsulation method was removed
10.6. draft-ietf-eai-downgrade: Version 03
o Followed draft-ietf-eai-utf8headers-03 and
draft-ietf-eai-smtpext-03
o Downgraded: and Envelope-Downgraded: headers definition was added
o Mail header downgrading method was refined
o Examples in Appendix A were refined
10.7. draft-ietf-eai-downgrade: Version 04
o Followed draft-ietf-eai-utf8headers-06, draft-ietf-eai-smtpext-07
and draft-ietf-eai-dsn-02
o Downgrading requirements and conditions were moved to
Introduction.
o Descriptions about upgrading were removed.
o SPF and DKIM discussion were removed.
o Added many header fields downgrading.
o Allow address literal rewriting without alternate US-ASCII address
in header fields.
o Added MIME body part headers downgrading.
o Added ORCPT downgrading.
11. Normative References
[I-D.ietf-eai-dsn]
Newman, C. and A. Melnikov, "International Delivery and
Disposition Notifications", draft-ietf-eai-dsn-02 (work in
progress), July 2007.
[I-D.ietf-eai-framework]
Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", draft-ietf-eai-framework-05
(work in progress), February 2007.
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[I-D.ietf-eai-smtpext]
Yao, J. and W. Mao, "SMTP extension for internationalized
email address", draft-ietf-eai-smtpext-07 (work in
progress), June 2007.
[]
Yeh, J., "Internationalized Email Headers",
draft-ietf-eai-utf8headers-05 (work in progress),
April 2007.
[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.
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.
[RFC3461] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)",
RFC 3461, January 2003.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4021] Klyne, G. and J. Palme, "Registration of Mail and MIME
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Header Fields", RFC 4021, March 2005.
Appendix A. Displaying downgraded message
Displaying downgraded message is mostly retrieved by MIME decoding
[RFC2047][RFC2231]. Result of MIME decoding, downgraded address
header fields and undefined header fields are still in Downgraded:
headers, but it is MIME decoded. This decoded Downgraded: headers
contain the original headers and the recipient can read them. But
the recipient's MUA cannot use the original header fields
automatically.
Additionally, MUAs can decode Downgraded: header. It is described in
Appendix A.1 and Appendix A.2.
A.1. Displaying technique 1
MUA can remove 'Downgraded:' from decoded 'Downgraded:' header
fields. With this technique, The address header fields may be
displayed twice, one is ASCII-only downgraded header field and the
other is from decoded Downgraded: header.
A.2. Displaying technique 2
MUA can decode and regenerate headers which contains the original
non-ASCII addresses. It is described below:
o For each Downgraded: header, generate new header which field-name
is the second field of the Downgraded: header and the header value
is the third field of the Downgraded: header.
* If the header is an address header described in Section 5,
+ Generate ASCII only header defined in Section 5 from the
decoded header.
+ Remove the header field which is the same with the generated
ASCII only header from the header fields. If the headers
contain [RFC2047] encoded part, decode it before comparison.
Appendix B. Examples
B.1. Downgrading example 1
This section shows an SMTP Downgrading example. Consider a
downgradable mail message.
o The sender address is "NON-ASCII-FROM" which is non-ASCII address.
Its ASCII alternative is "ASCII-FROM".
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o The "To" address is "NON-ASCII-TO" which is non-ASCII address.
Its ASCII alternative is "ASCII-TO".
o The "CC" address is non-ASCII address "NON-ASCII-CC" without
alternative US-ASCII address.
o The Subject header is "NON-ASCII-SUBJECT" which contains non-ASCII
characters.
Original UTF8SMTP message SMTP session
MAIL From: <NON-ASCII-FROM> ALT-ADDRESS <ASCII-FROM>
RCPT TO: <NON-ASCII-TO> ALT-ADDRESS <ASCII-TO>
RCPT TO: <NON-ASCII-CC>
-------------------------------------------------------------
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: NON-ASCII-SUBJECT
From: <NON-ASCII-FROM <ASCII-FROM>>
To: <NON-ASCII-TO <ASCII-TO>>
CC: <NON-ASCII-CC>
Date: DATE
MAIL_BODY
Figure 3: Original UTF8SMTP message
In this example, there are two SMTP recipients, one is To:, the other
is CC:. In this example, assume the Cc: recipient's MTA supports
UTF8SMTP and the To: recipient's MTA does not support UTF8SMTP. The
SMTP downgrading treats To: session downgrading. Figure 4 shows SMTP
downgraded example.
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MAIL From: <ASCII-FROM>
RCPT TO: <ASCII-TO>
-------------------------------------------------------------
Envelope-Downgraded: From: <RFC2047(NON-ASCII-FROM)> <ASCII-FROM>
Envelope-Downgraded: To: <RFC2047(NON-ASCII-TO)> <ASCII-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: <NON-ASCII-FROM <ASCII-FROM>>
To: <NON-ASCII-TO <ASCII-TO>>
CC: <NON-ASCII-CC>
Date: DATE
MAIL_BODY
Figure 4: SMTP Downgraded UTF8SMTP message
After SMTP downgrading, header downgrading is performed. Final
downgraded messages are shown in Figure 5. Return-Path header will
be added the destination MTA.
Result of the header downgrading.
Return-Path: <ASCII-FROM>
Envelope-Downgraded: From: <RFC2047(NON-ASCII-FROM)> <ASCII-FROM>
Envelope-Downgraded: To: <RFC2047(NON-ASCII-TO)> <ASCII-TO>
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: RFC2047(UTF-8_SUBJECT)
Downgraded: From: RFC2047(<NON-ASCII-FROM <ASCII-FROM>>)
From: <ASCII-FROM>
Downgraded: To: RFC2047(<NON-ASCII-TO <ASCII-TO>>)
To: <ASCII-TO>
Downgraded: CC: RFC2047(<NON-ASCII-CC>)
CC: Internationalized address RFC2047(NON-ASCII-CC) removed:;
Date: DATE
MAIL_BODY
Figure 5: Header downgraded message
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RFC2047() stands for [RFC2047] encoding.
B.2. Displaying example (Displaying technique 1)
This example shows MIME decoded message of Figure 5.
Result of MIME decoding.
Return-Path: <ASCII-FROM>
Envelope-Downgraded: From: <NON-ASCII-FROM> <ASCII-FROM>
Envelope-Downgraded: To: <NON-ASCII-TO> <ASCII-TO>
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: UTF-8_SUBJECT
Downgraded: From: <NON-ASCII-FROM <ASCII-FROM>>
From: <ASCII-FROM>
Downgraded: To: <NON-ASCII-TO <ASCII-TO>>
To: <ASCII-TO>
Downgraded: CC: <NON-ASCII-CC>
CC: Internationalized address NON-ASCII-CC removed:;
Date: DATE
MAIL_BODY
Figure 6: MIME decoded message
B.3. Displaying example (Displaying technique 2)
This example shows displaying process of Appendix A.2 for Figure 5.
First, check 'Downgraded:' header existence.
Select 'Downgraded:' headers.
Downgraded: From: <NON-ASCII-FROM <ASCII-FROM>>
Downgraded: To: <NON-ASCII-TO <ASCII-TO>>
Downgraded: CC: <NON-ASCII-CC>
Figure 7: Displaying technique 2: selecting Downgraded headers
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Apply address header downgrading to the decoded header.
From: <ASCII-FROM>
To: <ASCII-TO>
CC: Internationalized address RFC2047(NON-ASCII-CC) removed:;
Figure 8: Displaying technique 2: downgraded decoded Downgraded
headers
Remove the header line which is the same with the downgraded line.
If the headers contain [RFC2047] encoded part, decode it before
comparison.
Return-Path: <ASCII-FROM>
Envelope-Downgraded: From: <NON-ASCII-FROM> <ASCII-FROM>
Envelope-Downgraded: To: <NON-ASCII-TO> <ASCII-TO>
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: UTF-8_SUBJECT
Downgraded: From: <NON-ASCII-FROM <ASCII-FROM>>
Downgraded: To: <NON-ASCII-TO <ASCII-TO>>
Downgraded: CC: <NON-ASCII-CC <ASCII-CC>>
Date: DATE
MAIL_BODY
Figure 9: Displaying technique 2: Removing duplicated headers
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Decode each 'Downgraded' header and replace it with its decoded
header. If each mail header has [RFC2047] encoded part and which
encoding is "UTF-8", it is a downgraded header, so decode it.
Return-Path: <ASCII-FROM>
Envelope-Downgraded: From: <NON-ASCII-FROM> <ASCII-FROM>
Envelope-Downgraded: To: <NON-ASCII-TO> <ASCII-TO>
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: UTF-8_SUBJECT
From: <NON-ASCII-FROM <ASCII-FROM>>
To: <NON-ASCII-TO <ASCII-TO>>
CC: <NON-ASCII-CC <ASCII-CC>>
Date: DATE
MAIL_BODY
Figure 10: Display technique 2: decoded message
As a result, in this simple example, all original header fields are
displayed in the original form.
B.4. Downgrading example 2
In many cases, the sender wants to use non-ASCII address and the
recipient does not support UTF8SMTP and does not have non-ASCII
address.
o The sender address is "NON-ASCII-FROM" which is non-ASCII address.
Its ASCII alternative is "ASCII-FROM".
o The "To" address is "ASCII-TO" which is ASCII only.
o The Subject header is "NON-ASCII-SUBJECT" which contains non-ASCII
characters.
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Original UTF8SMTP message SMTP session
MAIL From: <NON-ASCII-FROM> ALT-ADDRESS <ASCII-FROM>
RCPT TO: <ASCII-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: <NON-ASCII-FROM <ASCII-FROM>>
To: <ASCII-TO>
Date: DATE
MAIL_BODY
Figure 11: Original UTF8SMTP message 2
In this example, SMTP session is downgradable. Figure 12 shows SMTP
downgraded example.
MAIL From: <ASCII-FROM>
RCPT TO: <ASCII-TO>
-------------------------------------------------------------
Envelope-Downgraded: From: <RFC2047(NON-ASCII-FROM)> <ASCII-FROM>
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: NON-ASCII-SUBJECT
From: <NON-ASCII-FROM <ASCII-FROM>>
To: <ASCII-TO>
Date: DATE
MAIL_BODY
Figure 12: SMTP Downgraded UTF8SMTP message 2
After SMTP downgrading, header downgrading is performed. The
downgraded example is shown in Figure 13.
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Envelope-Downgraded: From: <RFC2047(NON-ASCII-FROM)> <ASCII-FROM>
Message-Id: MESSAGE_ID
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8bit
Subject: RFC2047(UTF-8_SUBJECT)
Downgraded: From: RFC2047(<NON-ASCII-FROM <ASCII-FROM>>)
From: <ASCII-FROM>
To: <ASCII-TO>
Date: DATE
MAIL_BODY
Figure 13: Header downgraded message 2
Authors' Addresses
Yoshiro YONEYA (editor)
JPRS
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065
Japan
Phone: +81 3 5215 8451
Email: yone@jprs.co.jp
Kazunori Fujiwara (editor)
JPRS
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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