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
(2) an extensible set of different formats for non-textual
(3) multi-part message bodies, and
(4) textual header information in character sets other than
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 fourth document, RFC 2048, specifies various IANA registration
procedures for the following MIME facilities:
(1) media types,
(2) external body access types,
Registration of character sets for use in MIME is covered elsewhere
and is no longer addressed by this document.
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.