AT&T is having trouble with their DNS services for e-mail IP address reverse lookup
While e-mailing someone with an sbcglobal.net, ameritech.net, prodigy.net, or any other legacy e-mail domain name owned by AT&T, we are getting reverse DNS error NDRs.
We have checked our reverse DNS settings, and can confirm that they are working properly. This may have something to do with the other issues being reported about AT&T internet services.
Hopefully this will be fixed quickly, a similar issue had been reported a few months ago on these forums, and via a blog. Please read the included link for more information.