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

Skip to content Primary navigationThe RFC SeriesFor AuthorsAbout UsHomeRFC 2046 View as: Plain Text, Compact HTML Info RFC 2046: Multipurpose Internet Mail Extensions (MIME) Part Two: Media Typesmedia typesNovember 1996. N. Freed, N. BorensteinDraft StandardSubscribe5 subscribed Add to Set Added to 3 Sets Read aloud This RFC was updated, see RFC 2646, RFC 3798, RFC 5147, RFC 6657, RFC 8098.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 6. Experimental Media Type Values ....................... 40 7. Summary .............................................. 41 8. Security Considerations .............................. 41 9. Authors' Addresses ................................... 42 Freed & Borenstein Standards Track [Page 2] RFC 2046 Media Types November 1996 A. Collected Grammar .................................... 43 1. Introduction The first document in this set, RFC 2045, defines a number of header fields, including Content-Type. The Content-Type field is used to specify the nature of the data in the body of a MIME entity, by giving media type and subtype identifiers, and by providing auxiliary information that may be required for certain media types. After the type and subtype names, the remainder of the header field is simply a set of parameters, specified in an attribute/value notation. The ordering of parameters is not significant. In general, the top-level media type is used to declare the general type of data, while the subtype specifies a specific format for that type of data. Thus, a media type of "image/xyz" is enough to tell a user agent that the data is an image, even if the user agent has no knowledge of the specific image format "xyz". Such information can be used, for exampl