I am getting a lot of spam recently that I am having a hard time getting flagged by spamassassin. We have enabled SPF checking and it works but I think these emails are getting through because the return-path is not from my domain.

Is there a way to get spamassassin to flag an email if the return-path and from field do not match?

Return-Path: stakespv07@scottiecd.com
Received: from by smtp.secureserver.net; Fri, 19 Feb 2010
From: user@mydomain.com
Subject: Very urgent
To: <user@mydomain.com>