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
datatracker.ietf.org