What technology can deal with spam, where the originator is actively and maliciously trying to break your filtering algorithm, but is helpless when dealing with bounce-backs, where there is no such intent?
Then you haven't looked very hard. Every CRM system worth its salt (including the free OTRS) supports this. Either by inserting a cookie into the initial mail ("please leave this line intact when you reply") or, smarter, by assigning a dedicated reply-to address to each recipient.
It's not rocket science and adding a "do not reply to this mail" speaks volumes about how little you care about customer service.
