Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
RFC 2046

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Network Working Group                                          N. Freed
Request for Comments: 2046                                     Innosoft
Obsoletes: 1521, 1522, 1590                               N. Borenstein
Category: Standards Track                                 First Virtual
                                                          November 1996

                 Multipurpose Internet Mail Extensions
                            (MIME) Part Two:
                              Media Types

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, but which 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. This 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-ASCII text

Freed & Borenstein          Standards Track                     [Page 1]
RFC 2046                      Media Types                  November 1996

   data in 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 and 1522, 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. Definition of a Top-Level Media Type .................    4
   3. Overview Of The Initial Top-Level Media Types ........    4
   4. Discrete Media Type Values ...........................    6
   4.1 Text Media Type .....................................    6
   4.1.1 Representation of Line Breaks .....................    7
   4.1.2 Charset Parameter .................................    7
   4.1.3 Plain Subtype .....................................   11
   4.1.4 Unrecognized Subtypes .............................   11
   4.2 Image Media Type ....................................   11
   4.3 Audio Media Type ....................................   11
   4.4 Video Media Type ....................................   12
   4.5 Application Media Type ..............................   12
   4.5.1 Octet-Stream Subtype ..............................   13
   4.5.2 PostScript Subtype ................................   14
   4.5.3 Other Application Subtypes ........................   17
   5. Composite Media Type Values ..........................   17
   5.1 Multipart Media Type ................................   17
   5.1.1 Common Syntax .....................................   19
   5.1.2 Handling Nested Messages and Multiparts ...........   24
   5.1.3 Mixed Subtype .....................................   24
   5.1.4 Alternative Subtype ...............................   24
   5.1.5 Digest Subtype ....................................   26
   5.1.6 Parallel Subtype ..................................   27
   5.1.7 Other Multipart Subtypes ..........................   28
   5.2 Message Media Type ..................................   28
   5.2.1 RFC822 Subtype ....................................   28
   5.2.2 Partial Subtype ...................................   29
   5.2.2.1 Message Fragmentation and Reassembly ............   30
   5.2.2.2 Fragmentation and Reassembly Example ............   31
   5.2.3 External-Body Subtype .............................   33
   5.2.4 Other Message Subtypes ............................   40