Reference

Constructing an Exim configuration file from scratch
This starts with "Hello World" in Exim, and moves on to build a useful configuration. It is one completed chapter of a dead book project.
http://shearer.org/en/writing/eximintro.html#Understanding%20Exim%20Configuration

Forums discussing Mail Servers and Proxy Servers software
Providing support for Eserv Mail Server users
http://forum.etype.net/

Free Mail Transport Agents Compared
This short article compares at the outermost level what are arguably the top four MTAs: Sendmail, qmail, Exim and Postfix. The author uses three of the four.
http://shearer.org/en/writing/mtacomparison.html

The IMAP Connection
Resources at the Univ. of Washington.
http://www.imap.org/

LAN Mail Protocols Summary FAQ
Access to IMAP (the Internet Message Access Protocol) resources at the University of Washington.
http://www.faqs.org/faqs/LANs/mail-protocols/index.html

Web-mail programs and discussion list
List of open-source Web-mail systems and a discussion list regarding these, and related matters of running mail systems for (typically) large numbers of people who need these because they are highly mobile, technical unsophisticated or because they do not have or want to rely on an ordinary ISP email account .
http://www.firstpr.com.au/web-mail/