If you want to delete spam at the server level you can add the following rule. You do need to have Spam Assassin installed on your account which can be done via your Site Manager.
* ^X-Spam-Level: \*\*\*\*\*\*\*\*\*\*
This code well delete any email that received a score of 10. The score is represented by the * (stars/asterisks). You can modify the amount of asterisks to accommodate your needs. This need to be added after the emails have been processed by Spam Assassin. On a WH account this would be after the line # END SPAMASSASSIN BLOCK