This article covers how to reject emails based on the spam score at SMTP time. This will prevent the server from sending out mail delivery failure notices for such spam emails.
1) Log in to WHM and navigate to the following location.
Home » Service Configuration » Exim Configuration Manager
2) Find the "Apache SpamAssassin™ reject spam score threshold" setting an set it to the span score you like to reject emails at. Email scoring higher than this will be rejected.
3) Click the "Save" button at the bottom of the page.