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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 Electronic Mail Standard Message Format: RFC 822
TCP/IP Electronic Mail RFC 822 Standard Message Format Processing and Interpretation
(Page 1 of 2)
The standards that define SMTP describe
the protocol as being responsible for transporting mail objects.
A mail object is described as consisting of two components: a message
and an envelope. The envelope contains all the information necessary
to accomplish transport of the message; the message is everything in
the e-mail message we have seen in the last two topics, including both
message header and body.
The distinction between these is
important technically. Just as the postal service only looks at the
envelope and not its contents in determining what to do with a letterno
wise-cracks, please! JSMTP
likewise only looks at the envelope in deciding how to send a message.
It does not rely on the information in the actual message itself for
basic transport purposes.
So technically, the envelope is not
the same as the message headers. However, as you can tell by looking
list of e-mail headers, each message includes
the recipients and other information needed for mail transport anyway.
For this reason, it is typical for an e-mail message to be specified
with sufficient header information that it can be considered enough
by itself to accomplish its own delivery. E-mail software can process
and interpret the message to construct the necessary envelope
for SMTP to transport the message to its destination mailbox(es). The
distinction between an e-mail message and its envelope is discussed
in more detail in the
topic describing SMTP mail transfers.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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