The Bayesian filter is very selective, and most of the emails it classifies will have probabilities that will be very close to either the upper or lower extremes, meaning very close to either 0% or 100%. That is normal, and is just the nature of the Bayesian filtering.

 

SpamFilter applies several different filters to incoming emails in a specific order to optimize performance. The Bayesian filter is the last one to be used by SpamFilter, and thus will catch a very small percentage of spam compared to the other filters. In our own ISP for example, the Bayesian filter used to catch only about 0.1% of spam, compared to 99.9% of the other filters (we disabled this filter a few years ago on our own live server). Adding to this, the Bayesian filters were “the thing” 9-10 years ago, and for a while this was the “star” filter in our SpamFilter. However the spammers have since learned how to easily bypass them, making the Bayesian filter even less effective. We often suggest disabling this filter for companies that receive large amounts of emails (~250,000 or more per day) as it does use a lot of resources with only minor gains.