One word about MailScanner, great.
It a tools that, well almost eliminate all your emails problem. Virus, and spam email will be eliminated. Not 100% though, but hey, nothing can.
MailScanner it a perl script that rely on other tools and software to eliminate virus and spam. It heavily rely on Spamassassin to check if the email is spam or not. For viruses, it can detect and use multiple anti virus installed, for example you can use clamav and f-prot for the same time.
MailScanner have many rules to simplify it setting. It have whitelist, blacklist, file name rules, file type rules and many others. For rbl, we can put it in mta level or in MailScanner. For example, we can put a safe rbl (which almost ONLY block spam) in mta level, and we put more agressive rbl in mailscanner. Very flexible.
You can configure MailScanner in most known mta server, like sendmail, postfix and exim. It very easy to install, my first try take me about 2 hours. And the server is up and running.
With the default configuration, it more than enough. to handle spam, but you tweak it if you like. The configuration is self explain, very easy to understand.
MailScanner it a very usefull software. If you are a mail administrator, its a must. The features is more powerfull than most paid software.
I will write more about mailscanner, very interesting software.
You can learn more about mailscanner at http://www.mailscanner.info