Integrated Online Solutions

2005.03.18 SPF and Mailman SpamAssasin

In the eternal struggle against spam, we have enabled SPF rules on our incoming mail server. "SPF":http://spf.pobox.com/ is a method of using DNS to identify whether email from an incoming IP realy is from the domain it claims to be from. This is far from foolproof, and not that many ISPs use it on their outgoing mail. However, some of the big ISPs do use it (such as AOL and the likes) which are huge victims of forged email. So now, for example, any email claiming to be from aol.com which does not connect to our server from one of the IPs that AOL itself specifies in its SPF settings will be rejected. We are already seeing a massive reduction in spam our mail server has to process due to this (thousands and thousands of messages per day). If mail is rejected due to the SPF policy, the sender will receive a bounce message which contains a URL pointing them to detailed information regarding why their mail was rejected, and what can be done about it. In other news, we now have enabled SpamAssassin on all of our hosted Mailman based mailing lists. The treshhold for rejection is set to 8 (somewhat high); messages scoring 5 or greater will be "held". Mail posted from members of the list get 3 point bonus, to help prevent false positives.