MailScanner is a Virus scanner for MTA's. It can be set up with at least Sendmail and Exim

MailScanner can be found here.

It also tends to ship with SpamAssassin, which is a spam filter.

I noticed wierd problems with MailScanner and Exim. It give odd errors when queueing an incoming mail - say things like "Remote host is local host" or "Retry timeout exceeded". I'm still not sure what caused these, but I found out when they happen, which explains why no one else sees the problem:

I use pine on the same machine as the MTA. Pine uses a "local" transport (shows up in the logs as local-esmtp). This was the only transport causing problems. If I used SMTP from another machine, or forced pine to use smtp via setting its smtp_server setting, it was fine. If I sent mail from the cmdline via 'mail' it was fine.

Wierd. :)