An alternative method to the rule-based filtering that MailWasher Pro offers is Bayesian filtering. This method works as a proxy so your email client collects email through it rather than connecting directly to the email server. Email filtering is performed using statistical analysis on the email that you've received before. In order for this to work you must maintain two distinct pools of emails; one for spam emails and another for non-spam emails. Basically, the Bayesian filters learn by analysing the wording used in the emails that you receive. Because of this, these filters are very effective on an individual basis because they work on the spam you get rather than what other people get.

The Bayesian filter application I favour is SpamWeed, mainly because it works with almost any POP email client, even includes set up instructions for my chosen email editor, The Bat!, and because it comes pretrained meaning it's ready to use out-of-the-box. A fully trained system takes time to build. For some people, this will be a faster process than for others, but users have shown this method to be over 99% accurate so it's well worth the effort. The training process itself is easy to do. If you spot a misclassification of a particular email then you just move it across to the correct pool. SpamWeed learns from this and takes it into account immediately.

On a similar note, if you don't have any anti-virus software running then you should take a look at the free version of AVG Anti-Virus Free Edition.

Why do they do it?

You might wonder why people would go to all this trouble in order to send out a few junk emails that are usually trashed as soon as they're recognised as being spam. Out of the many emails that they send out, although the vast majority will be deleted, a small percentage are successful in creating direct sales. Even if they don't succeed in getting you to part with any money if they've been able to confirm that your email address is live then that's worth something to someone e.g. another spammer who is willing to purchase a list of live email addresses.

Because the means by which spammers work have become relatively cheap, having only a small percentage of success makes it all worthwhile. So until every email user learns to deal with spam appropriately then the spammers will continue spamming.