Filtering spam with Exim and Spamassassin (properly)
SpamAssassin is a frequently used companion for Exim. However, most people set it up in a synchronous manner – spam is checked directly when the SMTP session is opened. While this is certainly a valid technique, it has it’s drawbacks. It leaves the server vulnerable to DOS attacks because the spam filtering is a big resource hog. Having SpamAssassin headers in the mail from the remote servers is also an issue, because the
$h_X-Spam-* variables will start misbehaving suddenly.
Fixing RDNS_NONE with Spamassassin
When dealing with SpamAssassin and Exim, one may often encounter a mysterious RDNS_NONE
Filtering spam with Exim only
Defense against spam has always been a hassle. Statistical filters only get you so far and they consume a LOT of resources. For exactly that reason I like to employ basic checking policies before accepting e-mail at all. These policies have gotten me pretty far and my false positive rate is pretty low.
The Big Exim Tutorial
In September 2009 I created the big Exim tutorial consisting of 5 parts on the Hungarian Unix Portal. In January 2010, I transfered it to my Hungarian site. Now I’m translating it to English.