Chapter 24. Mail Protocols
IN THIS CHAPTER
How Internet e-mail is sent and delivered
SMTP, POP3, and IMAP protocol server features
Message formats, parts, and encodings
A survey of various servers and clients
This chapter discusses the various technologies required to send e-mail over the Internet. Three important IP protocols form the core of these services: the Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP3), and Internet Message Access Protocol (IMAP). Together they form a system that is used to send mail from one e-mail client to another through two intervening e-mail application servers. The mechanism for polled e-mail is described.
E-mail messages consist of a header and a body. Different fields in the header are used for addresses. The SMTP protocol is used to format e-mail messages. This application protocol adds an envelope that is used by the SMTP server for routing. The Multipurpose Internet Mail Extensions, or MIME (which is an extension to SMTP), is used to segment and format e-mail messages as well as to include rich media content. The method by which MIME encodes non-ASCII or binary data is described.
A variety of e-mail clients are described. E-mail clients can support either POP3 or IMAP and offer a range of features that make getting e-mail from an incoming mail server more convenient and more secure. Other e-mail clients exist in the form of Web mail and terminal or telnet clients.
POP3 is used by clients to get e-mail from a POP3 server where the e-mail ...
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