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12/04/2005 Archived Entry: "winning the war on spam"

I've been contemplating the effectiveness of my anti-spam strategy. So far it seems to be working.

I have two "public" email addresses -- that appear on web pages -- and one private. Public address "A" gets processed by an older edition of SpamAssassin, which merely tags suspect messages "spam" and passes them on to my email client. Thunderbird then applies its Bayesian filter to the untagged messages.

Before the outbreak of the Sober worm, I'd receive about 40 spams a day at this account. SpamAssassin would tag about 1/3 of them, and Thunderbird would catch most of the rest, with only 2 or 3 slipping through to my Inbox to be deleted manually. Thunderbird is now sufficiently well trained that I get a false positive -- a legit message incorrectly tagged as spam -- less than once a month.

The last few days, address "A" has also been getting hammered with the Sober worm. In the last 24 hours, I've received 145 Sober emails. After a week of training, Thunderbird's Bayesian filter is now catching about 95% of them.

Public address "B" gets processed by a newer edition of SpamAssassin. In addition to using more effective rules, this filter deletes the spam messages rather than just tagging them and passing them through. (I have the threshold score set to a cautious 8.0 to avoid false positives.) As a result, on this account I see typically 3 or 4 spams a day; typically all but one will then be caught by Thunderbird's Bayesian filter.

Address "B" hasn't been hit with Sober at all. I believe this web host uses an antivirus filter on its mail server.

My "private" address was unspammed until about a month ago. Since then I have received two spam messages. I'm guessing that someone who has that address in his address book has been compromised by a computer virus. It's also possible that some firm I deal with has sold its email address list.

I'm wondering about the diminishing returns from adding a third level of spam filtering. But for now, spam has gone from being a problem to being a minor nuisance.


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