Are you using a secure mail key in TB in place of the account password?

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

How can I tell?

If the entry in Saved Passwords is the account password, it's not a secure key. Create a secure key on the AT&T site and use that instead of the account password.

In either case, where are those entered (since there is no prompt)?

If there's already an entry in Saved Passwords, right-click, Edit. Or, delete it, restart TB, enter the key when prompted.

This for 'normal password' authentication. I think OAuth2 authentication might be supported for AT&T in TB 140, in which case enter the account password in the OAuth window when prompted.

"If there's already an entry in Saved Passwords,........"

That is the whole point. Please read first post, where it states: "Deleted passwords and cannot see where to create them again, as it never prompts me for new ones."

What is the authentication method on the incoming and outgoing? Confirm that before trying to figure out why you aren't prompted. I'm assuming there is no VPN or security software in your setup. Also, confirm your other server settings are as in the support article.

All confirmed. But please give reasoning for comments.

The reason? To eliminate the possibility the issue is caused by a simple factor such as an incorrect setting or an interfering external app. Is your current profile one that has been used in many earlier versions of TB? Sometimes the presence of an obsolete file can cause passwords to malfunction. Adding the account to a new profile is one way to test.

Okay, so sure, I already understood all that. However, the idea of the presence of an "obsolete file" is a little odd. The upgraded programming of each new version is supposed to take care of that, or the programmers will have a lot of problems. The fact is, I've never run across such a thing, and, in any case, it does not appear to have anything to do with my described situation. The passwords are not malfunctioning; rather it appears that the program is. It seems to not know that there is no password present, and so attempting to connect without recognizing that fact is an indication of a serious problem.

Oh, wait a minute, that clearly indicates a bug. I need to report that.

Thanks.

Bug report at https://bugzilla.mozilla.org/show_bug.cgi?id=2017320

Whilst you would use a standard password to access webmail account, AT&T insist a Pop account must use a secure mail key for third party email clients. You would use that instead of the password that gets access to webmail. So whilst at this point you cannot enter it - you do need to create it.

At this point, I do not see that you have posted an image showing your current server settings. Can you please confirm the current server settings by uploading an image of 'Account Settings' > 'Server Settings' for the effected account. This is a frequent issue in many cases, so, please humour me and post info so we can properly rule it out.

The error message sounds like a connection with server was attempted, but never obtained, so server could not ask for password, so no prompt for password was displayed. Eventually it timed out.

That means the question is 'why does it not connect to server'.

Possible reasons- can you check the following and report back on results.

1. Network error: try restarting computer NetworkManager: Maybe the network interface is not routing traffic correctly.
2. Firewalls maybe blocking specific ports that are used by the IMAP or POP protocol: Access Firewall and make sure Thunderbird is set up as an allowed program.
3. Wrong server settings - need to be certain so first need to see what is being used - supply image.
4. A VPN is enabled, so server is blocking access as your IP is hidden. - Check whether a VPN has been auto enabled without you being aware of it. SWitch it off.
5. DNS IPv6 problem: Try disabling it.

In Thunderbird

• Settings > General
• Scroll to bottom and click on 'Config Editor; button
• It opens in a new tab
• In top search type: ipv6
• Look for: network.dns.disableIPv6
• Toggle from False to True
• Restart Thunderbird

Info in Bug report - It seems the issue was related to a VPN There was an enabled Kill Switch A VPN kill switch is a security feature that automatically disconnects you from the internet if your VPN connection drops. Looks like it's possible the VPN connection dropped and the Kill Switch reacted to disconnect traffic. Hence a Network error, unable to access server, a timeout, no request for password.

Net result was - Server seemed to be ok with a VPN, but if a VPN connection issue had occured then the Kill Switch would have disconnected access to internet etc.

The complaint seems to be about a lack of useful information on understanding errors when things go awol.

Useful to know to watch out for a possible VPN Kill Switch that can cause issue.