Linux Email Filtering With Spamassassin
Spamassassin is another good Linux add-on. As the name suggests, it is an anti-spam package.
It is implemented via procmail, the same as ClamAV. See my previous blogs on procmail and ClamAV.
Spamassassin is highly configurable. Whitelists to allow mail through, and blacklists to block mail, are supported. Where it really shines, however, is that it can use many different tools to determine if a message is spam, or not.
Among the tools available, are the ability to check blacklists via the Internet, as well as many built in scanners. Each of these scans results in a point value being assigned to the message. The higher the points, the more likely that the message is spam.
Procmail passes the message to Spamassassin, which processes it, adding headers for the points assigned, and passes it back to procmail. Procmail is configured to used these point headers to determine whether to pass the message on to the mailbox, or treat it as spam.
Messages can be marked as spam, by changing the subject line, or dropped completely. The approach that I like to take, is that low scoring messages are assumed to be non-spam. Messages with a middle score are tagged as possibly being spam, but delivered to the mailbox, in case they are not. Finally, high scoring messages are either deleted, or dropped into a catch-all file for later checking.
Spamassassin can be configured to use most of the very successful universal spam analysis databases: FSpamlist, BotScout, Project Honey Pot, SPAMHAUS, Stop Forum Spam, and other databases. With these databases a range of 90 – 100% success can be achieved with little maintenance needed.
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