I currently use Mailwasher or XTerminator as my Spam filters as they only download the headers and can delete the emails from the server.
This saves me time when I am on dialup and getting loads of spam.

Recently I have been reading more about Bayesian filters and how they are better than black/white lists.

Are there any free Bayesian filters that don't have to download the whole email?
Or is it necessary by their very nature to need to download the emails before processing them?