Chapter 11. Pull Mail Protocols: POP and IMAP

E-mail is one of the most important network functions in use today. Whether it's used to send a memo to a co-worker across the hall or a correspondent across the globe, e-mail has come to be something we rely upon on a daily basis. Linux includes extensive support for several different e-mail protocols. This chapter covers one class of e-mail protocols that are known as pull protocols, because the mail recipient initiates the transfers. These protocols contrast with push protocols, in which the sender initiates the transfer. (Chapter 19, Push Mail Protocol: SMTP, covers the most common push mail protocol.) Because e-mail originates with a sender, push protocols are always involved in e-mail delivery. E-mail transfers, though, typically involve several weigh stations . Pull protocols come into the picture in the last stage of a transfer, or occasionally at an intermediate stage.

NOTE

Although this chapter comes before Chapter 19 in this book, you must have a working push mail server before a pull mail server will be useful. Most Linux distributions install a working push mail server by default, so you should have at least minimal functionality from the start. If you're having problems with your push mail system, or if you need to configure it in something other than the default way, you may need to skip ahead to Chapter 19 and then come back to this chapter.

This chapter begins with a discussion of pull mail protocols, including when you should use one, and an overview of the two pull protocols discussed in this chapter. The chapter then proceeds to a discussion of how to configure Linux to serve both of these two protocols. This chapter concludes with a look at Fetchmail, which functions as a pull mail client that can then forward mail to other destinations using push mail protocols.