Thanks for all the tips. Everything seems to be working well now. I've actually gotten complaints about it being TOO strict from friends who's stupid ISP's have gotten their mailservers blacklisted.
One last question, I opted to have the subject rewritten but, instead of just getting a changed subject, I get a whole new email with the old email as an attachment. If I try to forward this on to my account at spamcop, they can't find the headers. Should the headers be changed so? What's going on?