One Sender To Only One User - Email Ends Up In Bayesian Learning Folder Automatically

WE have a case that started Aug 7th... One user in our domain emails sent to another local domain user automatically gets assigned as spam and put into the Bayesian Learning Folder. In the Spam Filter settings, our local domain is whitelisted and the users email address is specifically whitelisted... No idea why this is happening what to do to stop it... suggestions?