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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                           9  TCP/IP Enhanced Electronic Mail Message Format: Multipurpose Internet Mail Extensions (MIME)

MIME Content-Type Header and Discrete Media: Types, Subtypes and Parameters 1 2 3 4 5 6 MIME Content-Transfer-Encoding Header and Encoding Methods

Multipart Message Structure

These rules seem rather complicated, but they really aren’t that bad; once you’ve seen a couple of multipart messages the structure will make sense. To help clarify, I have provided Figure 302, which shows graphically the overall structure of a multipart MIME message.

Figure 302: MIME Multipart Message Structure

A MIME multipart message consists of a set of main headers and a main body portion, like all messages. Within the main body are one or more body parts, each of which has its own body-part-specific headers followed by the body part itself; each body part is shown in blue. The Content-Type header of the message as a whole (highlighted in green) indicates that the message type is multipart, and the boundary parameter specifies the name of the delimiter, in this case just called “Delimiter” (how boring.) This delimiter is used to separate the body parts from each other and from the preamble and epilogue that begin and end the message body, respectively.

MIME Content-Type Header and Discrete Media: Types, Subtypes and Parameters 1 2 3 4 5 6 MIME Content-Transfer-Encoding Header and Encoding Methods

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Version 3.0 - Version Date: September 20, 2005

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