http://support.kerio.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=460
Resetting the Bayes
All components of the Bayes filter are located in the Kerio MailServer store directory under /spamassassin/bayes/. To reset the Bayes, simply rename, or delete the bayes folder, then restart Kerio MailServer.