AT&T has a Postmaster site, but it doesn't contain a comprehensive list of their inbound email domains, so I thought it might be useful to put something together and share it with the world.
Here's all the AT&T consumer email domains that I know of:
Note that AT&T users either do or used to read mail through the Yahoo! Mail user interface, which means that some Yahoo! Mail filters could come into play when sending to AT&T users. However, AT&T runs their own inbound email servers, with their own filters and their own blocking, so it's very possible to be specifically blocked by AT&T.
Special thanks to reader Laurence Marks, who provided most of this list in a past comment, and I only now realized it might be helpful to all if we broke it out to its own post. Thanks!
Are any domains missing? Leave a comment with corrections, feedback or questions.