Filter email in Apple Mail by a phrase in the full headers

Someone has been sending me spam by spoofing my email address as the sender in order to get through the spam filter. I've searched through the detailed headers and found a URL that all the spam seems to be coming from (atlas206.aol.mail.ne1.yahoo.com). I'd like to add that to the spam filter, but I can't, because Apple Mail doesn't look at the detailed headers for filtering, only whatever the official "sender" is. Is there any way to filter for a specific phrase in the full headers?