This is more of a bug than a feature. :-)

Every now and then it appears that the spam filter completely stops working. I'll wake up to 5-12 OBVIOUSLY spam messages in my inbox. This will happen for a few days in a row, then subside... only to reoccur a few weeks or months later. I move/mark all spam messages when received so I'm doing my part to train the filtering algorithm, is there anything else that can be done to address this?