what is your email address? (Just tell me the part that comes after @ sign)
are you using the same server address in outlook express? pop.att.yahoo.com ?
when you try to retrieve your messages in thunderbird, what error are you getting exactly? (you open your thunderbird, what happens exactly?)
please open your thunderbird
go to tools, and then account settings.
in server settings section
did you type your username, with @bellsouth.net (did you also include this part?)
I am happy to hear that sir,
Have a good day.