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The TCP/IP Guide
9 TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
9 TCP/IP Key Applications and Application Protocols
9 TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
9 TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
9 TCP/IP Electronic Mail Message Formats and Message Processing: RFC 822 and MIME
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TCP/IP Enhanced Electronic Mail Message Format: Multipurpose Internet Mail Extensions (MIME)
The RFC
822 e-mail message format is the standard
for the exchange of electronic mail in TCP/IP internetworks. Its use
of simple ASCII text makes it easy to create, process and read e-mail
messages, which has contributed to the success of e-mail as a worldwide
communication method.
Unfortunately, while ASCII text is
great for writing simple memorandums and other short messages, it provides
no flexibility to support other types of communication. To allow e-mail
to carry multimedia information, arbitrary files, and messages in languages
using character sets other than ASCII, the Multipurpose Internet
Mail Extensions (MIME) standard was created.
In this section I describe MIME and
how it is used for modern e-mail messaging. I begin with an overview
of MIME and discussion of its history and the standards that define
it. I describe the two overall MIME message structures and provide a
summary of the important MIME-specific headers. I then explain the important
MIME Content-Type header in more detail, and discuss MIME discrete
media types, subtypes and parameters. I discuss the more complex MIME
multipart and encapsulated message structures, and then the different
methods by which data can be encoded into MIME message bodies. I conclude
with the special MIME extension to allow support for non-ASCII characters
in ordinary e-mail headers.
 Background Information: MIME is a message format that augments the basic RFC 822 message format, rather than replacing it. This section assumes that you have basic familiarity with the RFC 822 format and the more important e-mail message headers.
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 Note: While MIME was developed specifically for mail, its encoding and data representation methods have proven so useful that it has been adopted by other application protocols as well. One of the best known of these is the HyperText Transfer Protocol (HTTP), which uses MIME headers for indicating the characteristics of data being transferred. Some elements of MIME were in fact developed not for e-mail but for use by HTTP or other protocols, and I indicate this where appropriate. Be aware, however, that HTTP only uses elements of MIME; there are important differences, and HTTP messages are not MIME-compliant.
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Version 3.0 - Version Date: September 20, 2005
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