If you were to log in, you'd be able to get more information on your fellow community member.
In addition to PostOffice, Sendmail, and Qmail there is another alternative that goes by the name of Intrastore.. which really promises a lot more than the various products mentioned above.. with a web interface.. and coming from the venerable CDC...this product is free on linux (availbale on other os's as well) for upto 250 users.. I have tried Intrastore and it works like a song receiving upto 1000 messages a minute on a DEC ALPHA..