Mail Server & NAT

We have a mail server at X.X.X.162, our BM public is at X.X.X.168. All is
working fine, except when we try to send mail to the Comcast network, their
mail server now rejects the mail with the message: "no reverse DNS (PTR)
entry for the X.X.X.168 IP".

They are correct, our mail server is at .162 and the PTR record for it is
there. I am thinking that our outgoing traffic carries the .168 IP due to
NAT.

What do others do to cope with this situation? Stick a PTR record on the
..168 IP? Am I correctly understanding the issue?