Email provides a fast, efficient delivery system for text-based messages. As with all applications on the Internet, it uses certain protocols to achieve this, as illustrated in Figure 3.1, “How email works”:
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SMTP (Simple Mail Transfer Protocol) is used to distribute mail between servers, and by the mail client to send the message initially;
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POP (Post Office Protocol) is used by the mail client to download messages and headers to a local computer from the mail server. POP is useful if you want to read your mail offline (ie not connected to your mailserver), as it downloads and stores your email on your own computer.
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IMAP (Internet Message Access Protocol) is used by clients to access mail directly on the mail server. With IMAP, the mail usually stays stored on the recipient's server until it is deleted - the mail client only views the mail, rather than downloading it.
