Using regular expressions to kill spam

I am using mailwasher to find spam. The spammer is using MY web host's domain server as the from address. The only common item is a return path with kj*@*.* The IPs are always different.
I want to create a filter to search the Return Path for kj*@*.* BUT I do not want to filter out URL. How can I exclude valid emails from myself? I am attaching a full spam header as a text file.

Thanks,
KJ