I suggest you ask Verizon. AOL is as far as I can tell using Yahoo infrastructure. Yahoo are in the process of enforcing oAuth authentication for accounts. oAuth for mail requires providers such as verizon to issue a "secret" for Thunderbird developers to use to implement it with their servers.

I really have no idea what is going on at mail mashup central, but I have my doubts verizon/aol/yahoo actually know what they are doing either. SO I would check with them first to see if they have had another hair brained idea.

Thanks for taking the time to reply.

I had a long email exchange with AOL Mail customer support. They tried to get me to migrate to IMAP, then just walked me through the content of their setup documentation, which I already knew. Beyond that they were no help.

Not sure who to try to ask in Verizon - since they moved verizon.net email to the AOL Mail platform they've been referring email questions to AOL Mail. Any ideas about how to reach a human at Verizon who knows anything and is willing to respond substantively will be gratefully received.

All I can suggest to confirm it is not software on your computer causing the issue is this;

• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

If that does not work out, logging the connection may provide some clues, post beck if you get to that point.

Thanks, Matt. A quick update:

I tried booting into safe mode with networking. But when Windows finished loading, networking was disabled, and when I tried to launch the Windows networking troubleshooter, it gave an error message to the effect "sorry, the troubleshooter doesn't work in safe mode". I booted again back into normal mode and took a break for dinner.

Coming back upstairs I see that Thunderbird is now retrieving my verizon.net email successfully, after a gap of about 24 hours.

I still don't understand what happened, so I don't think I can say that the problem is fundamentally resolved, only that I'm going to have to wait until it hits again before I can resume troubleshooting.

In the meantime, thanks for your help. Much appreciated!