PTR question

I have a client on my cPanel server that uses an Exchange email server at his company for mail. So I fixed the mx record on my server to point to his exchange server for mail. My question is: Since he uses qwest for the exchange mail server's internet connection, I need to call qwest to setup a reverse dns entry. Do I have them set it up as or just

Currently, he is able to send and receive mail with the exception of sending to the big boys like AOL and Comcast and DNS reports shows no PTR. Sending to AOL and comcast returns a " Unable to deliver the message due to a communications failure" error.