Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples
RFC 2049
Network Working Group N. Freed
Request for Comments: 2049 Innosoft
Obsoletes: 1521, 1522, 1590 N. Borenstein
Category: Standards Track First Virtual
November 1996
Multipurpose Internet Mail Extensions
(MIME) Part Five:
Conformance Criteria and Examples
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
STD 11, RFC 822, defines a message representation protocol specifying
considerable detail about US-ASCII message headers, and leaves the
message content, or message body, as flat US-ASCII text. This set of
documents, collectively called the Multipurpose Internet Mail
Extensions, or MIME, redefines the format of messages to allow for
(1) textual message bodies in character sets other than
US-ASCII,
(2) an extensible set of different formats for non-textual
message bodies,
(3) multi-part message bodies, and
(4) textual header information in character sets other than
US-ASCII.
These documents are based on earlier work documented in RFC 934, STD
11, and RFC 1049, but extends and revises them. Because RFC 822 said
so little about message bodies, these documents are largely
orthogonal to (rather than a revision of) RFC 822.
The initial document in this set, RFC 2045, specifies the various
headers used to describe the structure of MIME messages. The second
document defines the general structure of the MIME media typing
system and defines an initial set of media types. The third
document, RFC 2047, describes extensions to RFC 822 to allow non-US-
Freed & Borenstein Standards Track [Page 1]
RFC 2049 MIME Conformance November 1996
ASCII text data in Internet mail header fields. The fourth document,
RFC 2048, specifies various IANA registration procedures for MIME-
related facilities. This fifth and final document describes MIME
conformance criteria as well as providing some illustrative examples
of MIME message formats, acknowledgements, and the bibliography.
These documents are revisions of RFCs 1521, 1522, and 1590, which
themselves were revisions of RFCs 1341 and 1342. Appendix B of this
document describes differences and changes from previous versions.
Table of Contents
1. Introduction .......................................... 2
2. MIME Conformance ...................................... 2
3. Guidelines for Sending Email Data ..................... 6
4. Canonical Encoding Model .............................. 9
5. Summary ............................................... 12
6. Security Considerations ............................... 12
7. Authors' Addresses .................................... 12
8. Acknowledgements ...................................... 13
A. A Complex Multipart Example ........................... 15
B. Changes from RFC 1521, 1522, and 1590 ................. 16
C. References ............................................ 20
1. Introduction
The first and second documents in this set define MIME header fields
and the initial set of MIME media types. The third document
describes extensions to RFC822 formats to allow for character sets
other than US-ASCII. This document describes what portions of MIME
must be supported by a conformant MIME implementation. It also
describes various pitfalls of contemporary messaging systems as well
as the canonical encoding model MIME is based on.
2. MIME Conformance
The mechanisms described in these documents are open-ended. It is
definitely not expected that all implementations will support all
available media types, nor that they will all share the same
extensions. In order to promote interoperability, however, it is
useful to define the concept of "MIME-conformance" to define a
certain level of implementation that allows the useful interworking
of messages with content that differs from US-ASCII text. In this
section, we specify the requirements for such conformance.
Freed & Borenstein Standards Track [Page 2]
RFC 2049 MIME Conformance November 1996
A mail user agent that is MIME-conformant MUST:
(1) Always generate a "MIME-Version: 1.0" header field in
any message it creates.
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