Spam Filter Mechanics
Wise Choice
© Lead Image © Jakub Jirsak, 123RF.com
Spam filters have different modes of operation. Understanding how they work can help you choose which to use.
These days, the choice of spam filters comes down to Bogofilter [1] and SpamAssassin [2]. Other choices, like DSPAM [3], are no longer in development. A few other choices (e.g., SpamBayes [4]) are available, but when an email reader offers a plugin, it is almost always for either Bogofilter or SpamAssassin.
What is less often discussed is which filter is the best to use in which circumstances. Instead, most users simply nod solemnly when they read that both involve "Bayesian filtering." Most of us – including many who use the phrase – have no idea what Bayesian filtering is, but it sounds scientific and reassures us that either choice is acceptable.
In fact, learning that Bogofilter and SpamAssassin are "Bayesian" is useless for choosing between them. To call them Bayesian means nothing more than their structure is based on the 18th-century work of Thomas Bayes [5] in statistics and probability. More specifically, both apply Bayes' work by collecting words and assigning a probability that each word indicates spam. The more suspect words contained in an email, the greater the chance it is spam. However, to make an informed choice between spam filters requires considerably more detail.
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