The Rule Filter is a Plugin. That means it is not directly integrated in Spamihilator, but it can be used to block Spam mails.
The filter uses a configurable list of rules, that will be applied to incoming mails. Based on the result of the rule evaluation the filter moves the current mail to the Recycle Bin or renders it to the email client. If no rule can be applied the mail will be processed by the next filter in the list.
For a detailed description of possible rules have a look at rules.