[WEBDosser]

Like i said you have a compromised file somewhere..
I tried all this:

Upload all new vbulletin files & clean up the database - no effect
Ok so then i thought i will htaccess the forum dir (password protect it) nope still loads of emails bouncing back.

Right i will htaccess the whole website, still nope still emails

Ok then lets close the website from inside admincp right? .. wrong still loads of emails.

All righty then i will remove all hacks and plungins even delete their files.. Nope! still emails

OK disable plugins in the config.php file.. nope nothing worked.

So then i started to think maybe it was my server so checked all the setting and found nothing wrong with the server, maybe a few brute force attacks but that was all..

By this time his email account on his website was being filled that much that i got server admin emails warning me that that user has sent umteen thousand and was reaching their limit.

So because it was for a friend and he was not bothered about the few posts on there he said i could delete and he would start a fresh.. WOW no more emails..

Hope it helps..