I recall that Chris Wagner (ismgr%atchisonks!net) was asking for assistance and recommendations a 
few days ago on something similar to that found in this article.  Make sure you read the comments 
for hints w/ alternatives such as Debian, postfix and exim instead of RedHat, and sendmail.
Setting up server tools for spam- and virus-free mail

http://www.newsforge.com/software/03/11/19/1939223.shtml?tid=74&tid=82