24.5.0 - deleted mail account and have issues with a spurious New Folder

Question

Hi
I have been messing around with my Thunderbird data, so this problem is of my own making I think.
I deleted an email account using my provider setup area. This was an email account I had set up at the start when joining this provider and contained only test messages etc. and so was of no further use.
I had set up this email address in Thunderbird and after deleting the account with my provider I then removed the account in Thunderbird. All seemed to be OK.
Now, to confuse matters. I had previously set up a list of folders under Local Folders for filtered email in Thunderbird - I now moved them up into my main account by click/drag/drop onto the account name. Although this took a very long time (and unexpectedly used an enormous amount of bandwidth), the operation finally seemed to finish (although that was really hard to determine until I finally found the Activity Monitor).
Now, for the point of this posting:
After all of the above, I discovered that a spurious folder had been created under the INBOX of my main account, called 'New%20Folder=0' which I read as New Folder-0. I don't know at what point in the above that this folder appeared, but I *think* I must have dragged/dropped one of my folder moves on the INBOX instead of the account name field.
Now, dear readers, if you have got thus far, the crux of my problem. I can not delete this folder, when I try, I get the message
The current operation on 'New%20folder-0' did not succeed. The mail server for account ******* responded folder does not exist.
I have tried a whole bunch of things, altering settings in its Properties etc but nothing lets me delete it.
Question is: how can I delete it?

Answer 1

I would:
a) check on the email provider's website to check if it had copied there, and deal with it. Your mention of bandwidth implies this is an IMAP-connected account.
b) close Thunderbird, open its [https://support.mozilla.org/en-US/kb/profiles-tb?esab=a&s=profiles&r=1&as=s profile] and delete the offending folder there. You need to browse your profile for a while to understand its structure before doing anything rash.
On the whole, I discourage users from dragging folders about as you have done. By all means drag the ''contents'' (better yet, use multi-select, then right-click and "copy to" or "move to") but moving ''folders'' is IMHO an undefined operation with unpredictable outcomes. I've heard of users moving a folder from one account to another and finding that it still associates with (i.e. "belongs to") the original account.