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Linux Journal: Building an E-mail Virus Detection System for Your Network

Nov 20, 2001, 13:47 (4 Talkback[s])
(Other stories by Dave Jones)
"The basic outline of the system consists of using Bash scripts, metamail, grep, the Obtuse Systems' smtpd product, Samba and a command-line virus scanner. A flowchart-style diagram can be found in Figure 1. The Obtuse Systems' SMTP store and forward package is freely available at www.obtuse.com/smtpd.html. The current version as of this writing is version 2.0. The virus scanner I chose was McAfee Virus Scan for UNIX/Linux, but there are quite a few others to choose from. Some are free and some are not. Do make sure you choose one that sets exit status codes based on what it finds and that is well supported with frequent signature updates.

The system can be set up on an existing Linux firewall or a separate machine, if you do not already have a Linux firewall in place. If you choose to set up a separate machine as the e-mail firewall, it doesn't have to be very powerful. A 200MHz 586 with 32MB of RAM would be plenty. Our network is attached to the Internet via SDSL and is protected by a Mandrake Linux machine running IP masquerade. This design made it easy to set up the system on our current firewall machine. The internal e-mail system used is not important as long as it speaks SMTP or ESMTP. In our case, we use Novell's Groupwise product. All SMTP traffic (port 25) should be redirected from the SMTP port on the firewall to the machine you have set up as your e-mail firewall on the inside (or to the firewall itself in our case). Now let's move on to the actual setup."

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