Enabling bounce address tag validation (BATV)
Bounce address tag validation (BATV) is a method for determining whether a bounce message to an address in your protected domain is valid. This method helps to prevent backscatter spam, in which a bounce message to your organization contains a forged recipient address.
With BATV enabled, the sender address of outbound email is marked with a unique tag. A bounce message addressed to that sender is examined for the presence of that unique tag. If the tag is detected, the bounce message is cleared for delivery. A bounce message without the tag is blocked.