Mail Server Recommendations
There are two types of mail servers that you are likely to be concerned with:
(1) SMTP servers, also called "mail transport agents" (MTAs). Examples of these are Sendmail, Qmail, and Postfix. These also are integrated with "mail delivery" software, which takes care of storing mail on the local machine in the case where that is its final destination. See http://www.tldp.org/HOWTO/Mail-Administrator-HOWTO.html for more about MTAs.
(2) POP (Post Office Protocol) and IMAP (Internet Message Access Protocol) servers, which provide for remote access to email. Because users often move around and/or don't have the time and expertise to manage their own SMTP servers, organizations usually need to support remote mail access.
Sendmail is the traditional MTA for Unix-like systems. However I prefer Postfix (http://www.postfix.org/); it's easier to administer, has a much better track record for security, and is compatible with Sendmail.
Qmail is also a worthy contender. It pioneered the "Maildir" format for local mail storage in which messages are stored in individual files, as opposed to Sendmail's "mbox" format which stores a single large file for each user; Maildir is generally considered more robust. However I've found Qmail to be more difficult to understand and work with than Postfix. Postfix can also be configured to use Maildir storage.
In the remote-mail-access department, POP3 is the current standard version of POP. However the IMAP protocol is vastly superior, as it provides for remote manipulation of mail and mail folders on the server itself, as opposed to just downloading of mail to the client. This is a very real benefit to anyone who works with their email both at the office and at home. In spite of this POP3 remains very popular, perhaps because IMAP support in many mail clients has been immature and buggy.
Commonly-used IMAP servers are Cyrus (http://asg.web.cmu.edu/cyrus/) and Courier-IMAP (http://www.inter7.com/courierimap/). Cyrus is rather complex and intended to run on a dedicated machine – not a requirement for most of us. I use and recommend Courier.
While there is also a complete Courier mail server bundle that includes a MTA, we're just talking about the separate IMAP server here (which also includes a POP3 server). Courier happens to require Maildir mail storage, so you'll need to configure Postfix to support it.
Installation details for Postfix and Courier-IMAP are beyond the scope of this article, but the installation instructions included with both packages are excellent. See also http://www.tldp.org/HOWTO/HOWTO-INDEX/howtos.html for various HOWTOs that discuss these applications, and various aspects of mail in general (not to mention Linux issues in general).
Other mail-related servers that I like and use are Mailman (http://www.list.org/) for mailing lists, and SquirrelMail (http://www.squirrelmail.org/) for web access to mail.
Another important part of the email picture is of course the "mail client" or "mail user agent" (MUA), the program that the user runs to read and compose email. My own favorite mail client is KDE's Kmail. Mozilla's mail component is also quite decent, as is Gnome's Evolution. There are also very good text-mode MUAs such as Pine and Mutt.
Prepared 2002-11-12 by Rod Roark (http://www.sunsetsystems.com/)