Just wanted to point out, there are two sides to every story. MailScanner is an excellent piece of software, used by thousands of large sites (including Postfix) without any problems. For more information on this issue, please read:
The Politics behind Postfix and Mailscanner
http://wiki.mailscanner.info/doku.php?id=documentation:configuration:mta:postfix:politicsThat being said, personally, I run MailScanner with Sendmail on a separate box. MailScanner works great as an external "mail gateway", which can be a front-end to literally any mail server, including Microsoft Exchange. This removes all of the heavy load from the overhead of scanning messages for viruses and spam from the server that is being used to access user mailboxes and perform other Virtualmin functions, such as web sites, user databases, etc. As an added benefit, MailScanner can scan each message with multiple spam and virus scanners, including custom programs to filter out any type of unwanted messages, so ClamAV and SpamAssassin aren't the only options.
MailScanner also has an excellent free interface for managing all incoming and outgoing mail, determining and reporting spam, managing the queue, generating statistics and reports, etc. For more information on this program, including pretty screen shots, see:
http://MailWatch.SourceForge.net/Best of all, these programs integrate perfectly with Virtualmin!