Saturday, December 15, 2007

Mini tutorial on SpamAssassin

Here’s a selected list of just a few of the hundreds of terms blocked by SpamAssassin, the most widely used network-level filter.

(Note: SpamAssassin uses open-source technology aimed at UNIX systems. My non-techie interpretation of this is that network administrators can configure SpamAssassin however they want.)

Some common trigger words or phrases:

- subject line starts with “free”

- subject contains FREE in all caps

- the word “free” in certain phrases (free offer, free leads, free access, free preview)

- certain words like “guarantee” in all caps

- words like “unsubscribe,” “leave,” and other list removal phrases

- using font sizes that are 2 + or bigger

- background in an HTML email that isn’t white

- HTML font color is gray, red, yellow, green, blue, magenta or “unknown to us”

- claims compliance with spam regulations or with US Senate Bill 1618 or House Bill 4176

- urges you to call now or claims you can be removed from the list

- the phrases: what are you waiting for, while supplies last, while you sleep

- asks you to click below

- uses a Nigerian scam key phrase such as “million dollars”

- money back guarantee


How can you avoid all of these? The answer is you don’t have to. SpamAssassin uses a rules-based system to filter mail headers and body text.

Basically, it’s a point system that assigns positive (it’s spam) or negative (it’s not spam) scores to a long list of trigger words, phrases and message headers. You have to reach a certain total before your email message is classified as spam and diverted.

If you’re accumulating negative as well as positive points, you may be under the threshold. For example, using the phrase “if only it were that easy” assigns you +2.0 points. “Free preview” gives you +1.7 points while “free trial” gives you only +0.1.

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