what are your SMTP settings (outgoing server)? Shoud be: smtp.aol.com Port 465 SSL/TLS

Thank you for responding.

My Outgoing Settings for Thunderbird are:

 Server name: smp.aol.com
 Port: 465
 Connection security: SSL/TLS
 Authentication method: OAuth2

which is what you have above.

I would appreciate it if you have any other suggestion.

It is possible for the Firewall to have gone awol - it basically may not recognise the update as same program.

Exit Thunderbird Access Firewall

Is Thunderbird set up as allowed program? If no then it must be set up as allowed. Also check the Thunderbird Software Updater program is allowed as well

If already set up as allowed, then unset it/ block it and ok it. then access Firewall again and reset up as allowed and ok it. This should reset settings.

Start Thunderbird and see if you get connection.

This should rule if Firewall is being a pain.

What Anti-Virus are you using ?

Thank you for attempting to help.

I opened the Windows Firewall and Firefox was already allowed. I tried again and it still gives me the exact same message as above.

I opened the allowed apps in my security software, AVG, and added Firefox. I tried again and it still gives me the exact same message as above.

Something is odd here. Why would it suddenly stop working? I mean that I had not shut down my computer between usages of Firefox. Admittedly I had exited Firefox and opened it multiple times during the day, but I had not shut down the computer.

Why would UAuth2 suddenly be unacceptable to AOL Mail?

Again, any help would be appreciated.

Thank you for attempting to help. I opened the Windows Firewall and Firefox was already allowed. I tried again and it still gives me the exact same message as above. I opened the allowed apps in my security software, AVG, and added Firefox. I tried again and it still gives me the exact same message as above.

You mention 'Firefox', but you need to have Thunderbird as allowed.

Something is odd here. Why would it suddenly stop working? I mean that I had not shut down my computer between usages of Firefox. Admittedly I had exited Firefox and opened it multiple times during the day, but I had not shut down the computer.

Do you really mean you closed the browser called 'Firefox' ?

Why would UAuth2 suddenly be unacceptable to AOL Mail? Again, any help would be appreciated.

Good question. Check to see what you have got stored in the passwords section.

Menu icon > Settings > Privacy & Security Click on 'Saved Passwords' click on 'Show Passwords'

You should have an oauth:// line for the verizon email address account and you need to keep it. Do you see a 'mailbox:// and smtp:// line for the same verizon email address account ? If yes: select each of those lines and click on 'Remove' click on 'Close'

Exit Thunderbird and wait a few moments for background processes to complete. Start Thunderbird and report back on results.

I note that you mention AVG - it could be blocking access:

Open AVG AntiVirus Menu > Settings > Basic protection > click the green slider button above "Email shield" to disable it. See info at link with images: https://support.avg.com/SupportArticleView?l=en&urlName=AVG-Antivirus-email-signature&supportType=home

REstart Thunderbird - report on results.

Thank you for responding.

I screwed up. I should have been using "Thunderbird" throughout this discussion instead of the word "Firefox". My mistake.

As far as AVG, I tried the fix you described and nothing changed. I got exactly the same error message.

As for going to "Menu icon > Settings > Privacy & Security", I tried that and could not find the "Privacy & Security" tab. There is a "Privacy" tab and an "Update&Security" tab, but no "Privacy & Security" tab.

If it helps, I am using "Windows 10 Pro".

Again, thank you for your patience and help.

Yesterday Thunderbird was updated. It now works for me. I do not know it failed. I do not know why the update fixed the problem.

It was discovered there was a problem with anything using a yahoo server and the developers worked on a fix which was released fairly quickly.