Filter Observations

SpamButcher is a highly effective tool to stop spam e-mail. It is of course, not perfect. I am keenly aware of which and how many email messages slip past the filter.

On my most heavily spammed account, SpamButcher will typically catch about 150 pieces of spam daily, and miss between 3 and 6. That's about a 97% hit rate. Individual users will of course have varying experiences.

The spam that's best at avoiding the filters seems to be short, free of excess HTML, and avoids using commonly filtered phrases. For example:

From: spammer@spamcity.com
To: me@me.com
Subject:  just like in Canada

Hi Tim, I'm just getting back to you about that site I found to save money on pills.

It's at http://www.jiggojamofu.com

Open source mail blockers commonly make their filtering databases available. This makes it easy for spammers to verify they aren't using any common filter phrases. Note - I'm not trying to fault the open-source crowd here.

The junk mail filter currently does not use a DNS based blacklist by default. The end-user can opt to enable this. In theory a blacklist could help with messages that are hard to recognize as spam based on their content.

However, some recent research indicated that the publicly available filters would only make a minor difference in the filters ability to block junk email. Blacklists are being left off by default for now.

Interestingly, Yahoo has deployed a very effective IP based blacklist. Unfortunately they have not made it publicly accessible.

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