Internationalized Email Headers
RFC 6532

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• 13

Internet Engineering Task Force (IETF)                           A. Yang
Request for Comments: 6532                                         TWNIC
Obsoletes: 5335                                                S. Steele
Updates: 2045                                                  Microsoft
Category: Standards Track                                       N. Freed
ISSN: 2070-1721                                                   Oracle
                                                           February 2012

                    Internationalized Email Headers

Abstract

   Internet mail was originally limited to 7-bit ASCII.  MIME added
   support for the use of 8-bit character sets in body parts, and also
   defined an encoded-word construct so other character sets could be
   used in certain header field values.  However, full
   internationalization of electronic mail requires additional
   enhancements to allow the use of Unicode, including characters
   outside the ASCII repertoire, in mail addresses as well as direct use
   of Unicode in header fields like "From:", "To:", and "Subject:",
   without requiring the use of complex encoded-word constructs.  This
   document specifies an enhancement to the Internet Message Format and
   to MIME that allows use of Unicode in mail addresses and most header
   field content.

   This specification updates Section 6.4 of RFC 2045 to eliminate the
   restriction prohibiting the use of non-identity content-transfer-
   encodings on subtypes of "message/".

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc6532.

Yang, et al.                 Standards Track                    [Page 1]
RFC 6532             Internationalized Email Headers       February 2012

Copyright Notice

   Copyright (c) 2012 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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology Used in This Specification . . . . . . . . . . . .  3
   3.  Changes to Message Header Fields . . . . . . . . . . . . . . .  4
     3.1.  UTF-8 Syntax and Normalization . . . . . . . . . . . . . .  4
     3.2.  Syntax Extensions to RFC 5322  . . . . . . . . . . . . . .  5
     3.3.  Use of 8-bit UTF-8 in Message-IDs  . . . . . . . . . . . .  5
     3.4.  Effects on Line Length Limits  . . . . . . . . . . . . . .  5
     3.5.  Changes to MIME Message Type Encoding Restrictions . . . .  6
     3.6.  Use of MIME Encoded-Words  . . . . . . . . . . . . . . . .  6
     3.7.  The message/global Media Type  . . . . . . . . . . . . . .  7
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10

Yang, et al.                 Standards Track                    [Page 2]
RFC 6532             Internationalized Email Headers       February 2012

1.  Introduction

   Internet mail distinguishes a message from its transport and further
   divides a message between a header and a body [RFC5322].  Internet
   mail header field values contain a variety of strings that are
   intended to be user-visible.  The range of supported characters for
   these strings was originally limited to [ASCII] in 7-bit form.  MIME
   [RFC2045] [RFC2046] [RFC2047] provides the ability to use additional
   character sets, but this support is limited to body part data and to
   special encoded-word constructs that were only allowed in a limited
   number of places in header field values.

   Globalization of the Internet requires support of the much larger set