So for each client that runs the Acronis backup, they hane to have a PTR record in DNS?   The Acronis software is a standalone package that isn't controlled by a central server.  But, if all it takes is a PTR to each client machine on the network, that should be easy enough.

Ben,

After getting back to work I checked in our internal DNS and there are already both A and PTR records which were produced by our internal DNS server.  Our public IP does have A, MX and PTR records.  Is there somewhere else that you may be referring to?

Point the backup software  to route emails to  a internal smtp hub that does not do the reverse lookup.  Any domino server with the smtp task loaded can function as the hub

Check the Server mail configuration, SMTP Inbound, mail relay exception list.