Reverse DNS pointer record

First I know the rDNS/PTR record has to be set by the server host. My question is in my environment what name should that DNS setting have.

Server hostname = Bob.ThisDomain.org

Accounts on this Server
ThisDomain.org
ThatDomain.org
MyBestFriendSite.net
TheGuyIreallyDontlike.net

The rDNS/PTR right now is set to mail.thatdomain.org

I seem to be having issues sending email from some thatdomain.org to yahoo/AT&T. I have followed their guides to be more compliant but I question my rDNS setting.

If you want to PM me your actual domain, I could do some outside testing with dig. Otherwise, there are various online DNS testing tools if you want to DIY.