MailScanner and ClamAV.
These two open source items scan all mail (incoming AND outgoing) on your server for viruses and trojan horses automatically and can clean/delete/notify sender and receiver of any files found to contain a virus, etc.
There are two ways to go about this:
1) The easy but OLD files way
OR
2) The more difficult, but more current files way
The easy way:
Log into your server via SSH. Get the following file from Layer1.cpanel.net and decompress it.
http://layer1.cpanel.net/mailscanner...all-1.5.tar.gz
tar -xvzf mailscanner-autoinstall-1.5.tar.gz
cd mailscanner-autoinstall-1.5.tar.gz
./install
When the installer gets to the point where it says that it is installing the required Perl modules wait a short time and then press ENTER/RETURN to continue installation.
This will do everything you need.
If mail doesn't work after doing this, you can run the uninstaller in this same directory.
./uninstall
The problem is these files are OLD (better than nothing, but not guaranteed to catch all the recent viruses).
If you'd rather go with the more dangerous, but more up-to-date version, the installation notes and the files you need into a single download, you can get here:
http://captainshareware.com/cpMailScanner.tgz
With the changes I made, you only really need the documentation and if you follow the cut'n'paste docs, all files will be downloaded and installed as needed.
I need to warn everyone up-front:
Don't even attempt this if you live and die by e-mail and can't afford some mail server downtime.
I mean that. SH's helpdesk will always gladly attempt to assist you to restore Exim to working order if you screw it up, but don't expect them to undo the mess you've made over the last hour in a few minutes.
If you can't live with the risk, don't even try it.
http://cPanelplus.com/ does offer a "professional" install for $35 if you're in a rush and don't want to attempt this yourself.
Oh.. and don't forget backup EVERYTHING on your server before attempting this.
DO NOT use the CLAMAV module available in WHM 9.5E3 or later if you use MailScanner. I discuss the pros and cons of MS vs. CPANEL's ClamAV module in the install document.
Written by Aric