It's time for an update! Here's my latest list of all of the consumer email domains hosted by AT&T, as best I can tell, as of August 2021.
This now includes "currently.com", a newer portal and email domain that AT&T went live with in 2019. Though not listed on the AT&T email help website, I've also chosen to include "worldnet.att.net" which is AT&T's legacy email domain. I confirmed with AT&T back in late 2020 that while they won't be adding new users to that subdomain, they do have active users that are allowed to continue to utilize it.
Special thanks to reader Laurence Marks, who provided much of this information to me previously.
For more information about troubleshooting email sends to AT&T's consumer email domains, be sure to visit the AT&T Postmaster website. And if you're finding yourself blocked when sending mail to AT&T domains, Pinpointe explains here how to reach out and request unblocking.