Counteracting the spammers

SpamAssassin is doing a good job on my site. It successfully protects my users’ mailboxes for some years now. However, during the last months spamming has increased significantly around the world. Luckily, only few spam is getting through, but a handful of spam mails a day is already too much for the pampered user. So I searched for current enhancements. So far I had only used Debian Etch’s standard spamassassin and amavisd-new packages.

I consider greylisting as a solution for days where I see no other choice. I can imagine my users being confused because they receive an expected mail not immediately. So I installed three enhancements for SpamAssassin:

• FuzzyOCR
• A botnet detector
• Rules against stock spam

The first one is available from Debian ‘unstable’, whereas the other two simply go into /etc/spamassassin. The SpamAssassin Rules Emporium provides a lot of other rules I haven’t tried yet.

The rules are already having some hits adding a lot to the spam score of messages. Here are examples from within 24 hours:

FUZZY_OCR=7.000 (twice), FUZZY_OCR=8.000, FUZZY_OCR=9.000 (5 times), FUZZY_OCR=10.000 (twice), BOTNET_OCNNEJP=5 (3 times), BOTNET_SHAWCABLE=5, SARE_STOCK_MSG_ID2=2.22 (5 times), SARE_GIF_ATTACH=0.75 (16 times), SARE_GIF_STOX=1.66 (6 times), SARE_PROLOSTOCK_SYM3=1.66 (8 times), SARE_MLH_Stock1=1.66 (12 times), SARE_RMML_Stock26=1.12, SARE_MLB_Stock1=1.66 (3 times), SARE_MLB_Stock3=0.794 (7 times), SARE_LWOILCO=0.388 (twice), SARE_LWSYMFMT=1.66, SARE_PROLOSTOCK_SYM4=2.66, SARE_PROLOSTOCK_SYM1=1.66, SARE_LWSHORTT=0.794.

So, it was worth the no effort. For those who wonder why there are only few hits, Postfix is already doing most of the job by rejecting bad connections.