I just installed Thunderbird.  It took two days for my Inbox to display any messages in it.  Now finally it displays all my messages and I can open the latest 800 or so, but not the older ones.  I tried to move the latest 800 into another folder, and they disappeared from my Thunderbird Inbox, but didn't reappear in the folder that I moved them to.  Using Outlook webmail, I can see they are still in the Inbox.

And when I try to acces Outlook webmail while Thunderbird is running, I get an Error Signing In page.

I have about 8000 emails in my Inbox.  I tried marking them all as Unread using webmail, but it stops and the page says there's been a server error.  If I repeated the process, then more emails would be marked as unread, but eventually, I can't get more than 6900 marked now.

This has been going on for days and Thunderbird can't even receive new emails.  I don't think it can even log in.  And then when it fails to log in, I can't even log in using webmail.