For us to better investigate this issue, we will need some more information.

Could you please do the following?

1. Open the menu > Help > Troubleshooting Information, then click Copy text to Clipboard.
2. Go to https://pastebin.mozilla.org/, paste the clipboard by right clicking in the large text area, select paste from the menu, change the retention period to expire in 28 days, use the Paste Snippet button to create a page containing your info, then copy the resulting URL (address) of the page created.
3. Open a reply to this post, and paste the URL to your troubleshooting information you just copied.
4. Please also provide results for the following test on your system
   • Does Thunderbird work as expected in Thunderbird troubleshooting mode?
   • Does Thunderbird work as expected with your OS started in safe mode with Networking. Instructions for each operating system: Windows 10/11, Windows 8, Windows 7, OSX

https://pastebin.mozilla.org/Jsuf4HMe

i can now receive email; perhaps getting a new security mail key helped; however now i cannot send email.. thanks for the help

oops. i got one batch of emails, but now back to can neither send nor receive. Sending of password for user capydan@att.net did not succeed. Mail server pop.att.yahoo.com responded: [SYS/TEMP] Server error - Please try again later.

I can try and walk you through using yahoo to get ATt mail. But I think as usual ATT have messed up something and have no idea what they are doing.

For ATT mailkey, you have you use it for incoming and outgoing. Two passwords are recorded, not one.

However to use Yahoo instead of the ATT mess. It is a dreadful mess really involving DNS poisoning and pretending thing that are not, are.

First up change the mail server names and settings to those used by yahoo. https://help.yahoo.com/kb/SLN4724.html

Then place Thunderbird in offline mode (that is the ((0)) in the bottom left of the Thunderbird window.) Offline has a strike though.

Restart Thunderbird. This will allow you to return to the account settings without trying to get mail by being offline. Change the authentication method to oauth. This can not be done before the restart because Thunderbird only offers the method for selected mail servers, it is a cumbersome approach, but it works.

Now you can return Thunderbird to online mode and get mail. It should pop up some oath windows to authorize Thunderbird to access the account. These generally do not cause any issues unless someone or some thing has disabled cookies in Thunderbird. But they are a necessary step in the oauth process.

This essentially allows you to use your ATT email address as a yahoo login. BTW for the rest of us, we can log into yahoo mail using the att web site mail links.

After all that is done, I suggest you change the setting for DNS over HTTPS in settings to use that. That removes the ability to ATT to log what sites you are looking up and direct advertising based on that information. I suggest the same for your web browser.