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Versions: 00 01 02 03 04 05 06 07 08 rfc6857                            
Email Address Internationalization                           K. Fujiwara
(EAI)                                                               JPRS
Internet-Draft                                              Oct 15, 2010
Intended status: Standards Track
Expires: April 18, 2011


 Post-delivery Message Downgrading for Internationalized Email Messages
                draft-ietf-eai-popimap-downgrade-00.txt

Abstract

   The Email Address Internationalization (UTF8SMTP) extension allows
   UTF-8 characters in mail header fields.  POP and IMAP servers support
   internationalized email messages.  If a POP/IMAP client does not
   support Email Address Internationalization, POP/IMAP servers cannot
   send Internationalized Email Headers to the client and cannot remove
   the message.  To avoid the situation, this document describes a
   conversion mechanism for internationalized Email messages to be
   traditional message format.

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 18, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  New Header Fields Definition . . . . . . . . . . . . . . . . .  4
     3.1.  Unknown Header Fields' Preservation Header Fields  . . . .  5
   4.  Email Header Fields Downgrading  . . . . . . . . . . . . . . .  5
     4.1.  Downgrading Method for Each ABNF Element . . . . . . . . .  5
       4.1.1.  RECEIVED Downgrading . . . . . . . . . . . . . . . . .  6
       4.1.2.  UNSTRUCTURED Downgrading . . . . . . . . . . . . . . .  6
       4.1.3.  WORD Downgrading . . . . . . . . . . . . . . . . . . .  6
       4.1.4.  COMMENT Downgrading  . . . . . . . . . . . . . . . . .  6
       4.1.5.  MIME-VALUE Downgrading . . . . . . . . . . . . . . . .  6
       4.1.6.  DISPLAY-NAME Downgrading . . . . . . . . . . . . . . .  6
       4.1.7.  MAILBOX Downgrading  . . . . . . . . . . . . . . . . .  6
       4.1.8.  ENCAPSULATION Downgrading  . . . . . . . . . . . . . .  7
       4.1.9.  TYPED-ADDRESS Downgrading  . . . . . . . . . . . . . .  7
     4.2.  Downgrading Method for Each Header Field . . . . . . . . .  7
       4.2.1.  Address Header Fields That Contain <address>s  . . . .  7
       4.2.2.  Address Header Fields with Typed Addresses . . . . . .  8
       4.2.3.  Downgrading Non-ASCII in Comments  . . . . . . . . . .  8
       4.2.4.  Received Header Field  . . . . . . . . . . . . . . . .  9
       4.2.5.  MIME Content Header Fields . . . . . . . . . . . . . .  9
       4.2.6.  Non-ASCII in <unstructured>  . . . . . . . . . . . . .  9
       4.2.7.  Non-ASCII in <phrase>  . . . . . . . . . . . . . . . .  9
       4.2.8.  Other Header Fields  . . . . . . . . . . . . . . . . .  9
   5.  MIME Body-Part Header Field Downgrading  . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   7.  Implementation Notes . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  RFC 2047 Encoding  . . . . . . . . . . . . . . . . . . . . 11
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . . 13
     A.1.  Downgrading Example  . . . . . . . . . . . . . . . . . . . 13




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1.  Introduction

   Traditional mail systems, which are defined by [RFC5322], allow ASCII
   characters in mail header field values.  The UTF8SMTP extension
   ([I-D.ietf-eai-frmwrk-4952bis] and [I-D.ietf-eai-rfc5335bis] allows
   UTF-8 characters in mail header field values.

   If a header field contains non-ASCII characters, POP/IMAP servers
   cannot send Internationalized Email Headers to the client and cannot
   remove the message.  This message downgrading mechanism converts mail
   header fields to an all-ASCII representation.  The POP/IMAP servers
   can use the downgrading mechanism and send the Internationalized
   Email message as a traditional form.

   [I-D.ietf-eai-rfc5335bis] allows UTF-8 characters to be used in mail
   header fields and MIME header fields.  The message downgrading
   mechanism specified here converts mail header fields and MIME header
   fields to ASCII.

   This document does not change any protocols except by defining new
   header fields.  It describes the conversion method from the
   internationalized email messages that are defined in
   [I-D.ietf-eai-frmwrk-4952bis], and [I-D.ietf-eai-rfc5335bis] to the
   traditional email messages defined in [RFC5322].

   Message Downgrading may be implemented in POP server and IMAP server
   only.

   This document tries to define the message downgrading process
   clearly.

   Downgrading consists of the following three parts:


   o  New header field definitions

   o  Email header field downgrading

   o  MIME header field downgrading

   In Section 3 of this document, header fields starting with
   "Downgraded-" are introduced.  They preserve the original header
   fields.

   Email header field downgrading is described in Section 4.  It
   generates ASCII-only header fields.

   MIME header fields are expanded in [I-D.ietf-eai-rfc5335bis].  MIME



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   header field downgrading is described in Section 5.  It generates
   ASCII-only MIME header fields.

   Displaying downgraded messages that originally contained
   internationalized header fields is out of scope of this document.  A
   POP/IMAP client which does not support UTF8 extension does not know
   internationalized message format described in
   [I-D.ietf-eai-rfc5335bis].

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].

   All specialized terms used in this specification are defined in the
   Email Address Internationalization (EAI) overview
   [I-D.ietf-eai-frmwrk-4952bis], in the mail message specifications
   [RFC5322], or in the 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-frmwrk-4952bis].

   This document depends on [I-D.ietf-eai-rfc5335bis].  Key words used
   in those documents are used in this document, too.

   The term "non-ASCII" refers to a UTF-8 string that contains at least
   one non-ASCII character.

   A "UTF8SMTP message" is an email message expanded by
   [I-D.ietf-eai-rfc5335bis].

3.  New Header Fields Definition

   New header fields starting with "Downgraded-" are defined here to
   preserve those mail header field values that contain UTF-8
   characters.  During downgrading, one new "Downgraded-" header field
   is added for each mail header field that cannot be passed as-is to a
   POP/IMAP client that does not support UTF8 extension.  The original
   mail header field is removed or rewritten.  Only those mail header
   fields that contain non-ASCII characters are affected.  The result of
   this process is a message that is compliant with existing email
   specifications [RFC5322].  The original internationalized information
   can be retrieved by examining the "Downgraded-" header fields that
   were added.





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3.1.  Unknown Header Fields' Preservation Header Fields

   The unknown header fields' preservation header fields are defined to
   encapsulate those original header fields that contain non-ASCII
   characters and are not otherwise provided for in this specification.
   The encapsulation header field name is the concatenation of
   "Downgraded-" and the original name.  The value field holds the
   original header field value.

   The header field syntax is specified as follows:


   fields     =/ unknown-downgraded-headers ":" unstructured CRLF

   unknown-downgraded-headers = "Downgraded-" original-header-field-name

   original-header-field-name = field-name

   field-name =  1*ftext

   ftext      =  %d33-57 /           ; Any character except
                 %d59-126            ;  controls, SP, and ":".


   To encapsulate a header field in a "Downgraded-" header field:

   1.  Generate a new "Downgraded-" header field whose value is the
       original header field value.

   2.  Treat the generated header field content as if it were
       unstructured, and then apply [RFC2047] encoding with charset
       UTF-8 as necessary so the result is ASCII.

   3.  Remove the original header field.

4.  Email Header Fields Downgrading

   This section defines the conversion method to ASCII for each header
   field that may contain non-ASCII characters.

   [I-D.ietf-eai-rfc5335bis] expands "Received:" header fields;
   [RFC5322] describes ABNF elements <mailbox>, <word>, <comment>,
   <unstructured>; [RFC2045] describes ABNF element <value>.

4.1.  Downgrading Method for Each ABNF Element

   Header field downgrading is defined below for each ABNF element.
   Downgrading an unknown header field is also defined as ENCAPSULATION



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   downgrading.  Converting the header field terminates when no non-
   ASCII characters remain in the header field.

4.1.1.  RECEIVED Downgrading

   If the header field name is "Received:" and the FOR clause contains a
   non-ASCII address, remove the FOR clause from the header field.
   Other parts (not counting <comment>s) should not contain non-ASCII
   values.

4.1.2.  UNSTRUCTURED Downgrading

   If the header field has an <unstructured> field that contains non-
   ASCII characters, apply [RFC2047] encoding with charset UTF-8.

4.1.3.  WORD Downgrading

   If the header field has any <word> fields that contain non-ASCII
   characters, apply [RFC2047] encoding with charset UTF-8.

4.1.4.  COMMENT Downgrading

   If the header field has any <comment> fields that contain non-ASCII
   characters, apply [RFC2047] encoding with charset UTF-8.

4.1.5.  MIME-VALUE Downgrading

   If the header field has any <value> elements defined by [RFC2045] and
   the elements contain non-ASCII characters, encode the <value>
   elements according to [RFC2231] with charset UTF-8 and leave the
   language information empty.  If the <value> element is <quoted-
   string> and it contains <CFWS> outside the DQUOTE, remove the <CFWS>
   before this conversion.

4.1.6.  DISPLAY-NAME Downgrading

   If the header field has any <address> (<mailbox> or <group>) elements
   and they have <display-name> elements that contain non-ASCII
   characters, encode the <display-name> elements according to [RFC2047]
   with charset UTF-8.  DISPLAY-NAME downgrading is the same algorithm
   as WORD downgrading.

4.1.7.  MAILBOX Downgrading

   The <mailbox> elements have no equivalent format for non-ASCII
   addresses.  If the header field has any <mailbox> elements that
   contain non-ASCII characters, rewrite each <mailbox> element to
   ASCII-only format.  The <mailbox> element that contains non-ASCII



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   characters is one of two formats.


   [ Display-name ] "<" Utf8-addr-spec ">"

   Utf8-addr-spec

      Rewrite both as:
      [ Display-name ] "Internationalized Address " Encoded-word
      " Removed:;"
      where the <Encoded-word> is the original <Utf8-addr-spec> encoded
      according to [RFC2047].

   [[ Note: If the original non-ASCII address is a part of a group
   address, this rewriting may conflict the original DISPLAY-NAME.  This
   problem need to be fixed. ]]

4.1.8.  ENCAPSULATION Downgrading

   If the header field contains non-ASCII characters and is such that no
   rule is given above, encapsulate it in a "Downgraded-" header field
   as described in Section 3.1 as a last resort.

   Applying this procedure to "Received:" header field is prohibited.

4.1.9.  TYPED-ADDRESS Downgrading

   If the header field contains <utf-8-type-addr> and the <utf-8-type-
   addr> contains raw non-ASCII characters, it is in utf-8-address form.
   Convert it to utf-8-addr-xtext form.  Those forms are described in
   [RFC5337].  COMMENT downgrading is also performed in this case.  If
   the address type is unrecognized and the header field contains non-
   ASCII characters, then fall back to using ENCAPSULATION downgrading
   on the entire header field.

4.2.  Downgrading Method for Each Header Field

   Header fields are listed in [RFC4021].  This section describes the
   downgrading method for each header field.

   If the whole mail header field does not contain non-ASCII characters,
   email header field downgrading is not required.  Each header field's
   downgrading method is described below.

4.2.1.  Address Header Fields That Contain <address>s






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   From:
   Sender:
   To:
   Cc:
   Bcc:
   Reply-To:
   Resent-From:
   Resent-Sender:
   Resent-To:
   Resent-Cc:
   Resent-Bcc:
   Resent-Reply-To:
   Return-Path:
   Disposition-Notification-To:

   If the header field contains <mailbox> elements that contain non-
   ASCII addresses, perform COMMENT downgrading, DISPLAY-NAME
   downgrading, and MAILBOX downgrading.

   [[ Note: RFC 5322 does not allow group syntax in "From:", "Resent-
   From:", "Sender:", "Resent-Sender:", but proposed method uses group
   syntax.  This problem need to be fixed. ]]

4.2.2.  Address Header Fields with Typed Addresses

   Original-Recipient:
   Final-Recipient:

   If the header field contains non-ASCII characters, perform TYPED-
   ADDRESS downgrading.

4.2.3.  Downgrading Non-ASCII in Comments

   Date:
   Message-ID:
   Resent-Message-ID:
   In-Reply-To:
   References:
   Resent-Date:
   Resent-Message-ID:
   MIME-Version:
   Content-ID:
   Content-Transfer-Encoding:
   Content-Language:







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   Accept-Language:
   Auto-Submitted:

   These header fields do not contain non-ASCII characters except in
   comments.  If the header field contains UTF-8 characters in comments,
   perform COMMENT downgrading.

4.2.4.  Received Header Field

   Received:

   Perform COMMENT downgrading and RECEIVED downgrading.

4.2.5.  MIME Content Header Fields


   Content-Type:
   Content-Disposition:

   Perform MIME-VALUE downgrading and COMMENT downgrading.

4.2.6.  Non-ASCII in <unstructured>


   Subject:
   Comments:
   Content-Description:

   Perform UNSTRUCTURED downgrading.

4.2.7.  Non-ASCII in <phrase>

   Keywords:

   Perform WORD downgrading.

4.2.8.  Other Header Fields

   For all other header fields that contain non-ASCII characters, are
   user-defined, and are missing from this document or future defined
   header fields, perform ENCAPSULATION downgrading.

   If the software understands the header field's structure and a
   downgrading algorithm other than ENCAPSULATION is applicable, that
   software SHOULD use that algorithm; ENCAPSULATION downgrading is used
   as a last resort.

   Mailing list header fields (those that start in "List-") are part of



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   this category.

5.  MIME Body-Part Header Field Downgrading

   MIME body-part header fields may contain non-ASCII characters
   [I-D.ietf-eai-rfc5335bis].  This section defines the conversion
   method to ASCII-only header fields for each MIME header field that
   contains non-ASCII characters.  Parse the message body's MIME
   structure at all levels and check each MIME header field to see
   whether it contains non-ASCII characters.  If the header field
   contains non-ASCII characters in the header field value, the header
   field is a target of the MIME body-part header field's downgrading.
   Each MIME header field's downgrading method is described below.
   COMMENT downgrading, MIME-VALUE downgrading, and UNSTRUCTURED
   downgrading are described in Section 4.

   Content-ID:
      The "Content-ID:" header field does not contain non-ASCII
      characters except in comments.  If the header field contains UTF-8
      characters in comments, perform COMMENT downgrading.

   Content-Type:

      Content-Disposition:  Perform MIME-VALUE downgrading and COMMENT
                            downgrading.

      Content-Description:  Perform UNSTRUCTURED downgrading.

6.  Security Considerations

   A downgraded message's header fields contain ASCII characters only.
   But they still contain MIME-encapsulated header fields that contain
   non-ASCII UTF-8 characters.  Furthermore, the body part may contain
   UTF-8 characters.  Implementations parsing Internet messages need to
   accept UTF-8 body parts and UTF-8 header fields that are MIME-
   encoded.  Thus, this document inherits the security considerations of
   MIME-encoded header fields ([RFC2047] and [RFC3629]).

   Rewriting header fields increases the opportunities for undetected
   spoofing by malicious senders.  However, rewritten header fields are
   preserved into Downgraded-* header fields, and parsing Downgraded-*
   header fields enables the detection of spoofing caused by
   downgrading.

   The techniques described here invalidate methods that depend on
   digital signatures over any part of the message, which includes the
   top-level header fields and body-part header fields.  Depending on
   the specific message being downgraded, the following techniques are



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   likely to break: DomainKeys Identified Mail (DKIM), and possibly
   S/MIME and Pretty Good Privacy (PGP).  The two obvious mitigations
   are to stick to 7-bit transport when using these techniques (as most/
   all of them presently require) or to make sure to have UTF8SMTP end-
   to-end when needed.

   While information in any email header field should usually be treated
   with some suspicion, current email systems commonly employ various
   mechanisms and protocols to make the information more trustworthy.
   Currently, information in the new Downgraded-* header fields is
   usually not inspected by these mechanisms, and may be even less
   trustworthy than the traditional header fields.  Note that the
   Downgraded-* header fields could have been inserted with malicious
   intent (and with content unrelated to the traditional header fields).

   See the "Security Considerations" section in
   [I-D.ietf-eai-frmwrk-4952bis] for more discussion.

7.  Implementation Notes

7.1.  RFC 2047 Encoding

   While [RFC2047] has a specific algorithm to deal with whitespace in
   adjacent encoded words, there are a number of deployed
   implementations that fail to implement the algorithm correctly.  As a
   result, whitespace behavior is somewhat unpredictable in practice
   when multiple encoded words are used.  While RFC 5322 states that
   implementations SHOULD limit lines to not more than 78 characters,
   implementations MAY choose to allow overly long encoded words in
   order to work around faulty [RFC2047] implementations.
   Implementations that choose to do so SHOULD have an optional
   mechanism to limit line length to 78 characters.

8.  IANA Considerations

   IANA is requested to refuse registration of all field names that
   start with "Downgraded-".  For unknown header fields, use the
   downgrading method described in Section 3.1 to avoid conflicts with
   existing IETF activity (Email Address Internationalization).

9.  Acknowledgements

   This document draws heavily from the experimental in-transit message
   downgrading procedure described in RFC 5504 [RFC5504].  The
   contribution of the co-author of that earlier document, Y. Yoneya,
   are gratefully acknowledged.

10.  References



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10.1.  Normative References

   [I-D.ietf-eai-frmwrk-4952bis]  Klensin, J. and Y. Ko, "Overview and
                                  Framework for Internationalized
                                  Email",
                                  draft-ietf-eai-frmwrk-4952bis-10 (work
                                  in progress), September 2010.

   [I-D.ietf-eai-rfc5335bis]      Yang, A. and S. Steele,
                                  "Internationalized Email Headers",
                                  draft-ietf-eai-rfc5335bis-02 (work in
                                  progress), August 2010.

   [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.

   [RFC2979]                      Freed, N., "Behavior of and
                                  Requirements for Internet Firewalls",
                                  RFC 2979, October 2000.

   [RFC3629]                      Yergeau, F., "UTF-8, a transformation
                                  format of ISO 10646", STD 63,
                                  RFC 3629, November 2003.




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   [RFC3864]                      Klyne, G., Nottingham, M., and J.
                                  Mogul, "Registration Procedures for
                                  Message Header Fields", BCP 90,
                                  RFC 3864, September 2004.

   [RFC4021]                      Klyne, G. and J. Palme, "Registration
                                  of Mail and MIME Header Fields",
                                  RFC 4021, March 2005.

   [RFC5322]                      Resnick, P., Ed., "Internet Message
                                  Format", RFC 5322, October 2008.

   [RFC5337]                      Newman, C. and A. Melnikov,
                                  "Internationalized Delivery Status and
                                  Disposition Notifications", RFC 5337,
                                  September 2008.

10.2.  Informative References

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

Appendix A.  Examples

A.1.  Downgrading Example

   This appendix shows an message downgrading example.  Consider a
   received mail message where:

   o  The sender address is a non-ASCII address,
      "NON-ASCII-local@example.com".  Its display-name is "DISPLAY-
      local".

   o  The "To:" header field contains two non-ASCII addresses,
      "NON-ASCII-remote1@example.net" and
      "NON-ASCII-remote2@example.com" Its display-names are "DISPLAY-
      remote1" and "DISPLAY-remote2".

   o  The "Cc:" header field contains a non-ASCII address,
      "NON-ASCII-remote3@example.org".  Its display-name is "DISPLAY-
      remote3".

   o  Four display names contain non-ASCII characters.

   o  The Subject header field is "NON-ASCII-SUBJECT", which contains
      non-ASCII characters.



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   o  There is an unknown header field "X-Unknown-Header" which contains
      non-ASCII characters.



   Return-Path: <NON-ASCII-local@example.com>
   Received: from ... by ... for <NON-ASCII-remote1@example.net>
   Received: from ... by ... for <NON-ASCII-remote1@example.net>
   From: DISPLAY-local <NON-ASCII-local@example.com>
   To: DISPLAY-remote1 <NON-ASCII-remote1@example.net>,
       DISPLAY-remote2 <NON-ASCII-remote2@example.com>
   Cc: DISPLAY-remote3 <NON-ASCII-remote3@example.org>
   Subject: NON-ASCII-SUBJECT
   Date: DATE
   Message-Id: MESSAGE_ID
   Mime-Version: 1.0
   Content-Type: text/plain; charset="UTF-8"
   Content-Transfer-Encoding: 8bit
   X-Unknown-Header: NON-ASCII-CHARACTERS

   MAIL_BODY


                 Figure 1: Received message in a mail drop

   The downgraded message is shown in Figure 2.  "Return-Path:",
   "From:", "To:" and "Cc:" header fields are rewritten.  "X-Unknown-
   Header:" is encapsulated as "Downgraded-X-Unknown-Header:".























Fujiwara                 Expires April 18, 2011                [Page 14]


Internet-Draft             POP/IMAP Downgrade                   Oct 2010


   Return-Path: Internationalized address
    =?UTF-8?Q?NON-ASCII-local@example.com?= removed:;
   Received: from ... by ...
   Received: from ... by ...
   From: =?UTF-8?Q?DISPLAY-local?= Internationalized address
    =?UTF-8?Q?NON-ASCII-local@example.com?= removed:;
   To: =?UTF-8?Q?DISPLAY-remote1?= Internationalized address
    =?UTF-8?Q?NON-ASCII-remote1@example.net?= removed:;,
    =?UTF-8?Q?DISPLAY-remote2?= Internationalized address
    =?UTF-8?Q?NON-ASCII-remote2@example.com?= removed:;,
   Cc: =?UTF-8?Q?DISPLAY-remote3?= Internationalized address
    =?UTF-8?Q?NON-ASCII-remote3@example.org?= removed:;
   Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?=
   Date: DATE
   Message-Id: MESSAGE_ID
   Mime-Version: 1.0
   Content-Type: text/plain; charset="UTF-8"
   Content-Transfer-Encoding: 8bit
   Downgraded-X-Unknown-Header: =?UTF-8?Q?NON-ASCII-CHARACTERS?=

   MAIL_BODY


                       Figure 2: Downgraded message

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
















Fujiwara                 Expires April 18, 2011                [Page 15]