Could someone point to a tutorial or a pre-build distro that can act as a spam firewall?
We currently use a barracuda but the license is run up and I'm looking for a cheaper alternative.
You could have a look at MailScanner - it's a spam/AV filter based on SpamAssassin, ClamAV and a few other goodies.
MailScanner is an e-mail security and anti-spam package for e-mail gateway systems. It is not designed to be run on Microsoft Windows desktop PCs. Instead, it is designed to be run on mail servers operated by companies and internet service providers (ISPs) so that all their users and customers can be protected from one place. This avoids the need for any software to be installed on individual desktop PCs at all.
The software works with any Unix-based system and is compatible with a wide range of mail transports. It comes with support for any combination of 25 different virus scanner packages, including the free ClamAV scanner, and its design allows the use of multiple virus scanners in parallel to increase the level of security.
Protection against spam is mostly based on the widely acclaimed SpamAssassin package, which again is free and open source. It is supplemented with fast blacklist lookups that can be used to reject a large proportion of messages with minimal overhead.
Protection against malware is provided by a very wide selection of checks and tests, ranging from simple filename rules to content-based file type detection. It also incorporates one of the most sophisticated phishing detectors available anywhere. Many other checks and tests can also be run against messages, far too many to list here.
MailScanner is highly configurable using a very easy-to-use system of rulesets. Virtually every configuration option can, for example, be controlled on a per-user, per-domain or per-IP basis.
MailScanner is extremely easy to integrate into your existing mail transport system, requiring no modification of existing sendmail configurations. Other MTAs require only minor modifications to configuration files, and these are all well documented both online and in the MailScanner book, available direct from the MailScanner web site.