I have never encountered this message, and I'm not finding any useful historical information.

How much free disk space do you have available? What is your version number? Have you tried reinstalling?

I didn't want to reinstall because I was afraid all of my messages saved to folders would get nuked, but Geek Squad reinstalled and fixed the problem.

Then I came home and started working on a problem I've been having for a few months now where I could receive emails from my Spectrum account, but not send emails. In the past I had tried tech support for Thunderbird and Spectrum and multiple suggested fixes from the internet and none worked. Yesterday I found a suggestion on a forum that fixed it.

Crossed fingers, but things are working now.

> Yesterday I found a suggestion on a forum that fixed it.

And what suggestion is that?

The email sending problem? The combination of charter-mobile.charter.net port 587 connection security STARTTLS. I have to believe that months ago, when I went around and around with tech support about the sending issue that we tried this SMTP combination and it failed, so maybe it was the combination of reinstalling and then using this set up that finally fixed the problem.