IN THIS CHAPTER
Sending mail via SMTP
Choosing a mail client
One of the primary uses for Linux on the Internet (aside from Apache) is as mail servers—both from the position of an MTA (Postfix, sendmail, Exim, and so on) and an MDA (Cyrus, Qpopper, and so on).
The terms MTA, MDA, and MUA are generic ways of referring to the components in a mail system:
Mail Transfer Agent (MTA): The component of the mail system that handles the receiving and sending of mail over the SMTP protocol.
Mail Delivery Agent (MDA): Controls the delivery of mail into a user's mailbox. An MDA also deals with the presentation of mail to a user over POP3 or IMAP.
Mail User Agent (MUA): The component that the end user employs to read mail. This could be Evolution, Outlook,
mail, mutt, or any other choice of MUA on the market.
A few very popular MTAs have arrived on the scene, with the grandfather of them all being sendmail.
Linux is extremely well suited to the hosting of mail, and the authors have worked on very large mail infrastructures where Linux has been prevalent. This chapter discusses using Linux as a mail server, and focuses in particular on sendmail or Postfix as an MTA and Qpopper and Cyrus as MDAs.
When mail is sent to a user, many things have to happen behind the scenes. Here we take an example of Roger sending an e-mail to Justin at different ...