Lets start with what phantom folders? I have seen a lot of folk complain for instance about the all mail folder.

Matt, thanks for your response. My phantom folders are all under Local Folders. This started recently when I noticed that a subfolder I'd created was empty instead of containing the 3-4 emails I thought I'd placed in it. When I tried to put the emails back in it, they wouldn't go. In the course of playing around with the problem folder---deleting, re-creating, re-naming, etc., I ended up with 6 of the originally named folders and 2 of the re-named variants---8 phantom folders in all. (The odd strings of letters and numerals following the folder names appeared on their own.)

When I try to delete them, they will migrate to the Trash folder under Local Folders, and when I try to permanently delete them from there, they end up back as subfolders under Local Folders.

I've attached a screenshot of the 8 phantom folders where they are currently residing under Local Folders.

One final--and odd---aspect. A couple of weeks ago I'd had a similar experience but on a smaller scale. Two folders refused to be deleted and so I finally gave up on them and just left them in the Trash folder under Local Folders. Somehow, in the course of messing around with this latest problem, those two seem to have actually (knock on wood) disappeared!

Thanks for any advice or guidance.

click on the "open folder" button in troubleshooting information in the help menu. (to be sure your in the active profile folder) Close Thunderbird Click on the mail folder in the windows file manager window that opens. Now open the "local folders" folder you should be able to see your problem folders shown as files, delete them and any associated MSF file. Restart Thunderbird.

Now to cause. Do you have an anti virus that is actively scanning files in the profile while tey are being used by Thunderbird. Most people have and need an exclusion in the anti virus product to stop the rot.

If the folder is being managed as part of a synchronization set, either for cloud or local backup, you might find you are experiencing contention issues between the Thunderbird process and the backup or synchronization process.

Matt,

Thank you very much---that seems to have done the trick! I'm so glad to be rid of those annoying reoccurring files. I really appreciate your help.

As for the cause, I'm running Windows 10 and using the installed Windows Defender antivirus. I can try to figure out how to add an exception for Thunderbird, but I guess I'm a little hesitant to not have that protection. What are the risks and the likelihood of a problem if I add the exception? Maybe I should just wait and see if this becomes a recurring problem and with what frequency. Now that you've showed me the solution, employing it every now and then wouldn't be a big issue for me.

At any rate, thanks so much for your expert assistance---very kind of you.