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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

TCP/IP Electronic Mail Access and Retrieval Protocols and Methods 1 2 3 TCP/IP Post Office Protocol (POP/POP3)

Comparing E-Mail Access and Retrieval Models

Of the three, which is best? You should know better than to ask me that question. J Each has advantages and disadvantages, which is why it is good that we have these options rather than the single SMTP protocol for mail access.

Direct server access has the main benefits of instant speed and universal access from any location. It has the disadvantage that you must be online to read mail, and that it usually requires you to use UNIX e-mail clients that most people are not familiar with. However, the Internet Message Access Protocol (IMAP) can also be used for online access.

Offline access has the main advantages of simplicity and short connection time requirements; you can easily connect to the mailbox, download messages and then read them locally. But that makes this method somewhat inflexible, and poorly-suited to access from different machines. Still, it is right now the most popular access method, because simplicity is important; it is best typified by the popular Post Office Protocol (POP).

Disconnected access attempts to combine the advantages of offline and online access without combining their disadvantages, and does a pretty good job. The advantages are significant: the ability to quickly access mail and use it offline, while retaining and updating the mailbox on the server to allow access from different client machines. IMAP is the protocol popularly used for disconnected access. In the IMAP overview I explore its advantages over offline access, as well as its main disadvantages: complexity and far less universal support than POP (though acceptance of IMAP is slowly increasing).

Finally, in recent years, a somewhat new mailbox access method has become popular: e-mail access using the World Wide Web. This technique allows a user to access his or her mailbox from any computer with an Internet connection and a Web browser. It is a good example of “line blurring”, not only between the access models discussed here, but between TCP/IP applications, in this case the Web and e-mail.

TCP/IP Electronic Mail Access and Retrieval Protocols and Methods 1 2 3 TCP/IP Post Office Protocol (POP/POP3)