In Thunderbird I have unwanted folders such as Archives. I didn't put them there, they just appeared one day. I have tried everything but cannot seem to get rid of them.
Check the account settings.
There you should find folder settings in the left pain.
In the right pain you can uncheck the archive option.
Then click OK.After that, try right click the archive folder and choose delete.
Its possible that you accidentally hit the archive short cut button which is the letter A ::mike