I've just installed Thunderbird 78.4.3 (32-bit) on Windows 10 Pro 2004, build 19041.630. This is the first time I've used Thunderbird. I've transferred my emails from Windows Live Mail 2012 (via .eml and ImportExportTools NG), and I have more than 38,000 emails in my Inbox and more than 33,000 in Sent. I also have a number of local folders. If I move an email from Inbox to a local folder, it does not appear in the destination folder. However, if I search the destination folder for the email recipient, I find it. And if I then open the email, and mark it as unread, and ''then ''click into a different folder and then back into the destination folder, the email appears in the list. This is not a problem with every email addresses: an @sky.com email behaved properly, but several @gmail.com emails and an @tnt.com email vanished as described. The same thing happened when I sent an email: it did not appear in Sent until I did the Find-mark unread trick. Oddly, when I tested Thunderbird ''before'' I imported emails from Windows Live Mail 2012 .eml files, this didn't happen - the sent email appeared in the Sent folder. Any ideas gratefully received!