Spam is a real problem nowadays. A huge amount of the e-mail trasfered nowadays is unsolicited e-mail (spam).

In my inbox, for example about 70% of the daily e-mail I receive is just spam. We're lucky because we have a good anti-spam filter that classifies and sweap most of this rubbish out of the real inbox, but... How good an anti-spam filter is?

Altough it might seem obvious to you, the main thing you want to know about an anti-spam filter is that it is accurate. I mean that a filter is almost unuseful if it not only deletes spam but deletes good mail too. That is what is called "false positives". A false positive is a legitime e-mail flagged as spam by your spam filter.

A filter that doesn't catch spam is bad, but a filter that catches too much spam (I mean, does false positives) is even worse.

It's all about balance. As it is often saind in civil engineering colleges: "To build a bridge that doesn't fall is very easy. The difficult thing is to build one that almost doesn't fall". That's true for spam filters too: "To make an anti-spam filter that filters all the spam is easy: just wipe out everythig. The difficult thing is to make one that catches just the spam" :-)

One of the best anti-spam filters we've seen is the one embedded in GMail, Google's free mail service.

We found that this is quite usual in many hosting providers, for example. A lot of people is confy because they know that their hosting provider is taking care of their spam but... at what extent? We usually found too much strict spam filters that delete a lot of legitimate e-mail without it's owner knowing it.

You must pay attention to this kind of problem. Tell your provider not to raise the filter level too much or maybe you'll end up losing an important email some day and get in real trouble.