Stopping it at the source (Score 1)

I was the senior architect at a hosting company previously that had a lot of issues with spammers - It was always up to me top deal with SPEWS, ORBS, etc.. so I came up with a solution that really pissed off some customers but after explaining the situation and helping them get around things - spamming from our servers (45 of them) went down to nill... The solution was a hack to QMail that checked the "From" address and made sure that it was a valid account under the gievn users domain - if the system detected that the "From" address was not a real address, then it redirected the mail with an explanation of why, to the email address that the user signed up with... A couple of times the user did spam, and ended up filling his own earthlink mailbox with thousands of email before they realized what was going on...