Remove the entries from Saved Passwords for the AT&T account, restart TB, and when asked for a password, enter a secure mail key that you create on the AT&T website.

https://www.att.com/support/article/dsl-high-speed/KM1010523/

How do I know which to use? POP3 or IMAP?

Secure email key. I did that years ago. Where is it now? I'll have to do that all over? This is a waste of time. Why do I have to do this more than once? I always thought that once you entered and saved a password, that the only other work was to change it from time to time. Some web sites remind you to change it, and others don't. Typical inconsistency of the Internet. Some sites make you go through hoops to get in and others are super simple. And what really bothers me is I understand changing passwords on banks, etc. But some web sites have no reason to be secure. And I could go on. Ranting Raving So what is so special about ATT? Do they think they are kings? Do they want us to play all these silly games with "security". How darn secure should our email be? Don't we have A/V to take care of that? I know for a fact that my A/V scans all incoming and outgoing mail. Sorry about this.

WOW! I asked which ATT was, POP3 or IMAP. Answer is both or either. But when I tried adding it to TB, it came up for POP3 only? So I didn't need to know which. But why is it that ATT didn't know this? That ATT access on TB is POP3 ONLY.

OK. I found a handwritten note by myself with a 16 digit code, all alpha, all small case. Is that my "security key"? If so, what do I do with it? I don't see any notation of how I got that or what it's for. So if a 16 digit code is what is my "security key". Where do I go to use it? I tried using this "security key" as my password in TB when trying to Add ATT to TB. That didn't work. This is a nightmare!

Aw shucks. I just went in and created a new security key and now have ATT.net on TB. Solved.