Several months ago, I have noticed that several folders were missing in Thunderbird. These folders exist on Outlook as viewed with a browser. I could not force the addition of those folders. Sometimes, I could rename a folder and it would show content for some days before disappearing. I am also having problems that a folder exists with not individual email account, but two subfolders have their full content. I cannot use Thunderbird to add content to a folder with empty content, except for the working subfolders. I have tried "Repair Folder" with no success. If "Foothill.msf" exists, it has zero or little content. I can generate new folders. I've been running Thunderbird for decades without a problem this severe. **** Outlook via browser is now missing the Foothill folder, but one of the subfolders exists on Thunderbird.!