It sounds like you're trying to use the old POP3 protocol to retrieve your messages from AT&T. Unless this is a deliberate choice on your part for some reason, I highly recommend using the newer IMAP protocol whenever possible. Gmail is automatically configured as an IMAP account by Thunderbird, so this may explain the difference in your experience with the two services.

In the Account Settings window, highlight the AT&T account you've created and then select Remove Account in the menu shown by clicking the Account Actions button underneath the list on the left. Click Account Actions again and this time select Add Mail Account. When you fill in your information and click Next, you should see that AT&T is attempting to connect via POP3. By clicking the Manual Config button the incoming protocol can be changed to IMAP, and you can find everything you need to fill in those fields correctly from AT&T's knowledge base article found here:

https://www.att.com/esupport/article.html#!/dsl-high-speed/KM1010523

If you encounter issues, try just filling in the IMAP and SMTP server addresses and your full e-mail address in both the Incoming and Outgoing username fields, and setting all of the remaining dropdown menus to the Auto selection. This should poll the servers with all of the possible permutations of those settings until it finds the one that works.

I removed the account and entered the name and password for the same account and I get an error message "Thunderbird failed to find the settings for my email account" I tried it several times and re-test several times.

Okay, then let's try a slightly different configuration. Try setting it up like this, of course substituting your e-mail for the one shown.

I rebooted my computer and tried again to install my email. I didn't configure it for IMAP but Thunderbird found the configuration and I received all my emails. I hope it continues to work. Thanks for your help I'm going to bed.

It's a new day and it worked most of the day but not now. I tried your settings and as soon as I change from POP3 to IMAP the "done" box is grayed out and it won't add the account. What now?

It's Alex again. I found out I can send with the ATT/bellsouth account all the time. I installed the account and it's working with POP3 now.

Glad to hear it's working for you. If you want to try again with the IMAP protocol, you just need to re-test once changing the Incoming server to IMAP and adjusting the settings as shown in the screencap. Once it confirms they work you can click done and be on your way. It really is a superior way to manage your e-mails, POP3 is purely a legacy option at this time.

I put the folders I use in another account to keep them from being deleted. I tried to drag them into the old account and they wouldn't stick. I then created new folders and tried to install the old emails into them. Mozilla timed out before they were all into the new folders. How do I do it? Thanks.

If I do this all of the messages I have saved will disappear. They are not saved on the ATT server so I do I retain the messages?