Humphrey,

There are several mail server implementations out there for Linux/Unix.

When you say a "mail server", you mean at least three component applications being run on a computer to provide services. These are:

1. SMTP Engine - it accepts inbound mail and delivers it to our mailboxes. It also accepts mail from our users and either delivers it to our mailboxes or sends the mail out to the hostile Internet:)

2. POP3 Engine - Our Mail user applications (MuA), like Outlook, etc connect to this and retrieves mail for us to act on.

3. IMAP4 Engine - used as above but has all the mail residing on the server side. It's read from there, not quite retrieved.

Now that you know what a mail server entails, I can mention that there are several SMTP applications (free and commercial) and as well those applications that provide POP3 or IMAP4 (or both).

For SMTP, you have Sendmail, Exim, Postfix, Qmail, Courier (all Free) while for POP3/IMAP4, you have courier-imap (I think it was mistakenly named, because it provides both POP3 and IMAP4), tpop3d, dovecot, vm-pop3d, etc...

All it takes is to identify one that will sufficiently address your needs, read the documentation on implementation and you are good to go. All these applications have online support forums where you can ask particular questions regarding the daily administration.