If your current connection is not on the ATT network, a complaint like yours may happen.
I have a email account with AT&T and I am trying to use that account with Windows Live Mail and I am not having any luck. I have the right username and password, as well as the right server settings (according to AT&T's website). However, when I try send and receive mail it comes up and asks me to log in. After entering the email address and password it keeps popping back up. It will not let me proceed. After many attempts, it comes up with error code 0x800CCC90. I know that I am using the correct login information because I can log into webmail just fine.
Does anyone have any idea what might be causing this? I would like to point out that I also have another AT&T account that I use with Windows Live Mail and I have never had any problems with it.
I wonder if there is a problem with my email account settings with AT&T.