Set up your Filter Aggressiveness
By default these settings are set to No Preference this does not mean that the messages do not get filtered, it only means that you have no preference to request a message to have a higher score and pass, or a lower score and get stopped by the spam filter. If you find that too many spam messages are getting through the filter adjust the settings to aggressive, if too many valid messages are getting trapped lower your settings to lenient.
The Heuristics Engine is a new type of filtering that looks above the simple word match and knows bad IP’s, this filter changes all the time, and learns from each wave of spam that hits. We strongly recommend you leave this On.
Backscatter detection is set to Intelligent by default, this will help eliminate undeliverable email notices from emails you did not create reaching your inbox.