This same dude came back again today with a different IP and an account that I can't find as yet. His previous account is banned!
69.50.208.4 - - [13/Feb/2007:05:20:11 -0500] "POST /classifieds/contact.php HTTP/1.0" 200 1251 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; en) Opera 8.50"
The Opera 8.5 flags him as the same one. (I have my reasons.)
He popped out 22 more emails to my sellers!
He either had registered an earlier stealth account or he figured out how to send email through the server without logging in.
EDIT: If he was still logged in from the first time, could he send email even though he was banned in the forum registration system?
Evidently, at least in my system, banning a user does not prevent him from sending email responses through the classifieds. Changing his password does the trick. Banned SCAMMER sending email through ads.