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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 Access and Retrieval Protocols and Methods
9 TCP/IP Internet Message Access Protocol (IMAP/IMAP4)
IMAP General Operation, Client/Server Communication and Session States
(Page 1 of 3)
IMAP does the same basic job as POP:
it enables access to a mailbox stored on a remote server. For this reason,
it's not too surprising that IMAP is somewhat similar to POP in operation,
and you'll notice those similarities in this topic if you've already
read about POP3. However, IMAP has many more features and capabilities
than POP. Therefore, it's also not too surprising that IMAP would be
more complex than POP in terms of how it operates, and I think you will
notice this as well.
IMAP4 is a standard client/server
protocol like POP3 and most
other TCP/IP application protocols. For
the protocol to function, an IMAP4 server must be operating on the server
where user mailboxes are located. Again, as with POP3, this need not
necessarily be the same physical server as the one that provides SMTP
service. The mailbox must in some way be made accessible to both SMTP
for incoming mail and to IMAP4 for message retrieval and modification.
A mechanism for ensuring exclusive access to avoid interference between
the various protocols is also needed.
IMAP4 uses the Transmission
Control Protocol (TCP) for communication.
This ensures that all commands and data are sent reliably and received
in the correct order. IMAP4 servers listen on well-known
port number 143 for incoming connection
requests from IMAP4 clients. After a TCP connection is established,
the IMAP4 session begins.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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