If you're running a Windows server (I use Linux as a production server and Windows XP as a test server) iMail from Ipswitch is a simple to use mail server with lots of options.  It even includes a simple web server which runs on port 8383 (as I recall) offering simple web mail.  I've enjoyed tinkering with it and, of course, if you find it useful you can always support the developers by buying a copy - it' much more affordable than Exchange.  Hope folks find this useful.....  Various docs and shortcuts are included to help you get started.


IMail Server is an electronic mail solution for Internet and intranet
messaging requirements. Easy to install and administer, IMail
Server significantly reduces the cost of mail implementation and
administration. Its features improve productivity and provide an
alternative to proprietary systems or complicated UNIX-based
Internet mail.
IMail Server uses Simple Mail Transfer Protocol (SMTP) to send
and receive mail over the Internet or internal TCP/IP network.
There are also servers for LDAP, Finger, and Whois information.
The Web Administration capability of the Monitor server allows
system administrators to monitor the system and perform
maintenance using a web browser on any computer. They can
receive a notification when a service is down, and restart it.
IMail Server provides:
• Full integration with the Windows user database
• Ability to base user mail accounts on an external database
IMail Server e-mail can be read with:
• Any POP3 mail client
• Any IMAP4 mail client
• Any web browser
This Internet standards based client/server architecture provides
system administrators with flexibility to set up a mail solution that
easily accommodates different and/or geographically dispersed
mail clients.