Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
RFC 2045

Document Type RFC - Draft Standard (November 1996; Errata)
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Network Working Group                                          N. Freed
Request for Comments: 2045                                     Innosoft
Obsoletes: 1521, 1522, 1590                               N. Borenstein
Category: Standards Track                                 First Virtual
                                                          November 1996

                 Multipurpose Internet Mail Extensions
                            (MIME) Part One:
                   Format of Internet Message Bodies

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.

   This initial document specifies the various headers used to describe
   the structure of MIME messages. The second document, RFC 2046,
   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-ASCII text data in

Freed & Borenstein          Standards Track                     [Page 1]
RFC 2045                Internet Message Bodies            November 1996

   Internet mail header fields. The fourth document, RFC 2048, specifies
   various IANA registration procedures for MIME-related facilities. The
   fifth and final document, RFC 2049, 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.  An appendix in RFC
   2049 describes differences and changes from previous versions.

Table of Contents

   1. Introduction .........................................    3
   2. Definitions, Conventions, and Generic BNF Grammar ....    5
   2.1 CRLF ................................................    5
   2.2 Character Set .......................................    6
   2.3 Message .............................................    6
   2.4 Entity ..............................................    6
   2.5 Body Part ...........................................    7
   2.6 Body ................................................    7
   2.7 7bit Data ...........................................    7
   2.8 8bit Data ...........................................    7
   2.9 Binary Data .........................................    7
   2.10 Lines ..............................................    7
   3. MIME Header Fields ...................................    8
   4. MIME-Version Header Field ............................    8
   5. Content-Type Header Field ............................   10
   5.1 Syntax of the Content-Type Header Field .............   12
   5.2 Content-Type Defaults ...............................   14
   6. Content-Transfer-Encoding Header Field ...............   14
   6.1 Content-Transfer-Encoding Syntax ....................   14
   6.2 Content-Transfer-Encodings Semantics ................   15
   6.3 New Content-Transfer-Encodings ......................   16
   6.4 Interpretation and Use ..............................   16
   6.5 Translating Encodings ...............................   18
   6.6 Canonical Encoding Model ............................   19
   6.7 Quoted-Printable Content-Transfer-Encoding ..........   19
   6.8 Base64 Content-Transfer-Encoding ....................   24
   7. Content-ID Header Field ..............................   26
   8. Content-Description Header Field .....................   27
   9. Additional MIME Header Fields ........................   27
   10. Summary .............................................   27
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