Displaying Downgraded Messages for Email Address Internationalization
RFC 5825

Internet Engineering Task Force (IETF)                       K. Fujiwara
Request for Comments: 5825                                          JPRS
Category: Experimental                                          B. Leiba
ISSN: 2070-1721                                      Huawei Technologies
                                                              April 2010

 Displaying Downgraded Messages for Email Address Internationalization

Abstract

   This document describes a method for displaying downgraded messages
   that originally contained internationalized email addresses or
   internationalized header fields.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5825.

Copyright Notice

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

   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 Simplified BSD License.

Fujiwara & Leiba              Experimental                      [Page 1]
RFC 5825             Displaying Downgraded Messages           April 2010

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Converting Downgraded Message Headers for Display ...............3
      3.1. Considerations .............................................3
      3.2. The Process ................................................3
           3.2.1. No Reconstruction of the Envelope
                  Information Preservation ............................4
           3.2.2. Reconstructing the Address Header Fields'
                  Preservation Header .................................4
           3.2.3. The Unknown Header Fields' Preservation
                  Header Fields .......................................5
   4. Security Considerations .........................................6
   5. Acknowledgements ................................................6
   6. References ......................................................6
      6.1. Normative References .......................................6
      6.2. Informative References .....................................7
   Appendix A.  Examples ..............................................8
     A.1.  Displaying Example ........................................11

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 rejection of
   internationalized email messages, the downgrading mechanism [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 Mail User
   Agents (MUAs) or IMAP servers.  This document describes the
   restoration methods for 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