I have a zimbra server relaying through exchange (required for our firewall setup, network admin didn't want to add a rule since we are trying out zimbra first)

So the Exchange queue is filling up with all the NDRs from the zimbra server, basically says it can't connect to the domain to send the ndr.

In Exchange I can turn on reverse DNS to verify the domain before accepting the message. Is there anything like this in Zimbra that way it never accepts the message, because oviously the domain doesn't exist because it can't connect to send the NDR.

Any ideas?