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.
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.