How does a spam filter work?
There are two types of spam filter, one that blocks known spam and another that blocks new or unknown spam. Many anti-spam companies like Symantec Brightmail use honey pots, or fake email address to collect spam and create filters to stop that spam. MessageLabs uses Brightmail as one of its filters. For unknown spam, a heuristic algorithm is often used. It checks the structure of the email itself, how many people it is sent to, if it has links, phone number, and so on. Based on these factors, the algorithm decides is this email is spam or not. MessageLabs uses Skeptic to identify such spam.
