Archived Weblog Entry - 12/27/2004: "A week of SpamAssassin"

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12/27/2004 Archived Entry: "A week of SpamAssassin"

Happy Solstice, Hanukkah, Christmas, Boxing Day, Kwanzaa, etc., to all!

For the last week I've been conducting an experiment with our new spam filter. I'm quite impressed with its performance.

I have two "public" email accounts. Each gets from 10 to 20 spams a day. Account #1 is protected by an older version of SpamAssassin (2.63). Account #2, on our new web hosting service, is protected by the newer SpamAssassin 3.0.2. Any mail that gets through these filters gets processed by the Bayesian filter in Mozilla. Interesting results:


          caught by     caught by  false     false
Account   SpamAssassin  Bayesian   negative  positive
   #1          7           32         22        0
   #2         88            1          2        0

What a difference a new generation of SpamAssassin makes. On account #2 it let only 3 spams through, one of which was caught by Mozilla. This is not a reflection on Bayesian filters; SpamAssassin catches a lot of the "obvious" spam. More suggestive is the 3-out-of-5 performance of the Bayesian filter on account #1....a lot of spams are now being written to attempt to fool Bayesian filters. (They don't fool the final filter, which is me reading the subject line and sender.)

I'm also pleased to see that there were no false positives (legit emails mistakenly labelled as spam). Two ifeminist newsletters have had spam scores of 1.0 and 2.0, safely under the spam threshold of 8.0. I'm going to keep tracking this for a few more weeks, but it looks like I'll be able to use SpamAssassin to filter spam at the server and never download it to my PC.

brad