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MIME (Multipurpose Internet Mail Extension)

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

MIME is an IETF (Internet Engineering Task Force) standard originally defined in 1992 for sending a variety of different types of information (data types) via Internet electronic mail. Basically, MIME is what lets you attach just about any type of file to an Internet mail message. Previously, electronic mail messages could only handle text. What MIME does is provide standard ways to encode data types for transmission in electronic mail. MIME supports binary files, non-US-ASCII character sets, images, sound, video, and documents that are stored in special formats (such as compressed files). MIME also supports special fonts in the message itself.

A typical e-mail message consists of a header that includes the fields Data, To, From, and Subject, followed by the text of the message. RFC 1049 (A Content-Type Header Field for Internet Messages, March 1988) added a header that could describe a particular format for the message content, although the entire content had to be the same.

MIME's contributions are multipart attachments for messages and a way for users to choose the type of encoding they want to use. Each part of the message can hold a different data type. One way to understand MIME messages is to envision two or more separate e-mail messages, each with different data types, that are bundled together into a single message and going to the same destination. Each part of the message is called a body part and can contain text, graphics, audio, or video.

MIME adds information to the header of an e-mail message, such as the following:

  • MIME-Version    This indicates that the message conforms to MIME. This field is required.

  • Content-Type    This header indicates the type of data. Each body part in the message can be preceded by a Content-Type. There are seven major content types and a number of subtypes.

  • Content-Transfer-Encoding    This indicates the encoding method used on the body part.

  • Content-ID    This is an optional field that uniquely identifies a body part for reference elsewhere.

  • Content-Description    This is another option field that can be used to describe a body part.

Here is a listing of the primary RFCs that describe MIME.

  • RFC 2045 (MIME, Part One: Format of Internet Message Bodies, November 1996)

  • RFC 2046 (MIME, Part Two: Media Types, November 1996)

  • RFC 2047 (MIME, Part Three: Message Header Extensions for Non-ASCII Text, November 1996)

  • RFC 2048 (MIME, Part Four: Registration Procedures, November 1996)

  • RFC 2049 (MIME, Part Five: Conformance Criteria and Examples, November 1996)

  • RFC 2854 (The 'text/html' Media Type, June 2000)

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.