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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
9 TCP/IP Enhanced Electronic Mail Message Format: Multipurpose Internet Mail Extensions (MIME)
MIME Basic Structures and Headers
(Page 4 of 4)
Additional MIME Headers
In addition to the five basic headers
above, the MIME standard allows additional ones to be defined. The only
restriction is that they all must start with the word Content-,
which again, clearly labels them as describing content of a MIME entity
(message or body part). Obviously, both sender and recipient must support
a custom header for it to be useful.
Several new MIME headers have in
fact been created and documented in various Internet RFCs. Some are
actually designed not specifically for use by e-mail messages, but for
use by other protocols that make use of MIME technology, such as the
Transfer Protocol (HTTP). Here are three
In multipart MIME messages, this
header may be given to MIME body parts to control how information is
presented to the user. The two most common values are inline,
which says the content is intended to be displayed automatically along
with other body parts, and attachment, which indicates that
the content is separate from the main document. This header is defined
in RFC 2183.
Allows the location of a MIME body
part to be identified using a uniform
resource identifier (URI). This is sometimes
used when encoding HTML and other multimedia-enabled document formats
into e-mail using MIME multipart messages. It is defined in RFC 2557.
Specifies the length of a MIME entity
in bytes. This header is not commonly used in e-mail applications of
MIME, but is an
important header in HTTP. It is described
in the HTTP standards, first appearing in RFC 1945.
Key Concept: MIME provides flexibility in the information that can be carried in e-mail messages, by encoding non-ASCII data in ASCII form, and by adding special headers that describe this data and how it is to be interpreted. The most important MIME headers are Content-Type, which describes what sort of data is in the message, and Content-Transfer-Encoding, which specifies how the data is encoded. MIME supports two basic overall formats: simple structure, in which a single type of discrete media is encoded in a message; and complex structure, which encodes a composite media type that can carry multiple kinds of information.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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