Windows 10 What on Earth has happened

[jdl]

I got to thinking of a problem I had awhile back where messages I'd move would show back up in the original inbox. Rebuilding folders of course had no effect. One of the articles I saved had to do with rebuilding its cache.
Don't know if you've seen it or not, but I've kept the link handy just in case. Suddenly all emails are not visible | Thunderbird Support Forum | Mozilla Support

I ended up upgrading and haven't seen the problem since. Seems a lot of 'new' versions are a bit buggy. I've stayed at 78.10.1, which has been stable for me. Of course, a clean install may help clear things up. Backup your profile folder, then uninstall TB and start with a clean install.

 

[Gadzooks]

I've done all the actions mentioned in the link, and I'm afraid there is still no sign of the missing mails re-appearing.
I would like to close this thread, and to express my thanks for all the help and advice you good people have given.

 

[bochane]

You are welcome.

I still don't understand how opening webmail in a browser, which is supposed to do every thing outside your own computer, empties your local Thunderbird.
To get that done the server used by Thunderbird must have been emptied. That can be done by another email client connected to that server which uses the old POP protocol which may copy and delete all mail from the server. Nowadays one usually uses IMAP which synchronizes which the server.
But logging into webmail on the source server will never do that.
Thanks