I think something many sponsors probably need to spend time managing is their spam policy, publically stated somewhere on each site. Termination of said webmaster and not accepting spam traffic -- difficult to pass up the free traffic, but, when you are dealing with the anti-spam groups, it proves that you are not trying to make money off of it. And, SPF records. While the email may come from another address, and go directly to your main site, sometimes if they forge the returnpath in addition to the reply to, the SPF record would indicate that this mail is obviously not sanctioned. This has helped with spamhaus in the past and one other blacklist.
http://www.openspf.org/ for more info on adding SPF records.