Selecting this checkbox in Options | Incoming Mail | Options will enable Mailtraq to reject bounces to sent to 'users' who do not exist on your system.
Mailtraq provides backscatter mitigation to reduce the amount of spam your system has to manage.
What is Email Backscatter?
This term is used to describe the side-effect of email spam and email viruses, where an existing address from someone else is used as the sender address and large quantities of email is sent using that forged address. All non-delivery reports, vacation/out-of-office notices, challenge-responses, autoresponders, etc., end up with the forged sender address. The result is often hundreds or thousands of mails in the inbox of the innocent owner of that address. Wikipedia
[x] Reject bounces to unknown users
Available from Mailtraq build 2048: check your build here