With all the spam and viruses circulating the Internet these days, any network admin worth his or her salt will have appropriate filters in place to prevent these irritants from getting to users and customers. My predecessor, unfortunately, was worth far less than that, so my first task upon assuming the role of a systems administrator for a small ISP was to establish a mail filter. With no previous experience with a mail filtering system, I dug in and started my research. After reviewing open source solutions such as AmaViS and MailScanner and commercial solutions such as Postini and Mail Warden, I settled on Exim with the Exiscan-ACL plugin. . . .
With all the spam and viruses circulating the Internet these days, any network admin worth his or her salt will have appropriate filters in place to prevent these irritants from getting to users and customers. My predecessor, unfortunately, was worth far less than that, so my first task upon assuming the role of a systems administrator for a small ISP was to establish a mail filter.

With no previous experience with a mail filtering system, I dug in and started my research. After reviewing open source solutions such as AmaViS and MailScanner and commercial solutions such as Postini and Mail Warden, I settled on Exim with the Exiscan-ACL plugin.

We already had Exim in place on our FreeBSD servers, so the ability to stay with the same system rather than test something new had a lot of appeal. It had been installed a while back for performance and ease-of-use reasons, but had not been upgraded since version 3.36, now long obsolete. I also wanted an open source program if possible, as the fees for a commercial solution would have forced us to increase our service fees, which in turn may have cost us customers.

Exiscan is actually a patch for the Exim MTA (version 4), with installation on most systems requiring use of the patch command, though it is available as an RPM. FreeBSD users will find the Exiscan-ACL patch is already included in the Exim port. While a number of the other open-source filtering solutions are also included in the FreeBSD ports tree, the ability to maintain mail and scanning configuration in one configure file appealed to me.

The link for this article located at net-security.org is no longer available.