The Linux world has many excellent programs for handling email: Sendmail, Exim, qmail, and Postfix are the top four mail transfer agents (MTAs). This chapter covers Postfix. Like most of the post-Sendmail generation of MTAs, Postfix is designed from the ground up to be secureable and robust. It scales nicely from the single user who wants more control over her personal mail all the way up to the largest service provider.
Here’s a bit of terminology:
Mail transfer agent. This moves email between servers. Sendmail, Exim, qmail, and Postfix are MTAs. An MTA must support SMTP.
Simple Mail Transfer Protocol. This moves messages between mail servers.
Mail user agent, also called “mail client.” Mutt, Pine, Kmail, Evolution, and Balsa are MUAs. This is the user’s program for composing, sending, and receiving email. MUAs can fetch mail from a local folder, or from a remote server via POP and IMAP.
Mail delivery agent. This is an intermediary between an MTA and a MUA. Procmail and Fetchmail are two popular MDAs. An MDA is not required; it is used for extra functionality, such as filtering, sorting, and autoresponding.
Post Office Protocol. Moves messages from the server to the user’s inbox. A POP server is simple to operate and does not need a lot of horsepower.
Interactive Message Access Protocol. The message store remains on the server. An IMAP server needs a lot of RAM and lots of storage space.
Transport Layer Security ...