can not delete a sub folder

First follow this process. * Right click on sub-folder and select 'Delete' It should get moved into the 'Deleted' or 'Trash' folder. * Right click on the 'Deleted' / 'Trash' folder * select 'Empty Deleted/Trash'. * Close and restart Thunderbird. Did it come back? If yes: Make hidden files and folders visible. * http://kb.mozillazine.org/Show_hidden_files_and_folders In Thunderbird * Help > Troubleshooting Information * click on 'show folder' button a new window opens showing the contents of your profile folder name. * '''Close Thunderbird now - this is important.''' * Scroll down and delete this file: '''foldertree.json''' (a new one wil be created when you restart Thunderbird later). * click on 'Mail' folder * click on pop mail account name Sub-folders are kept in folders with a .sbd extension. Example: if the problem sub-folder is a subfolder of the Inbox; click on 'Inbox.sbd' folder So you would need to apply the same logic to locate the problem sub-folder. The sub-folder you want to delete will not appear as a 'Folder', but it will have the same name as your sub-folder. It will be an mbox 'File' (which has no extension). There will also be an index file with a .msf extension. * delete both the mbox file and the .msf file of same name. So if your Folder Pane structure was something like this: mail account name > Inbox > > Bills > > > > Gas > Friends > > Bob > > Anne example to locate 'Gas' In the profile mail account name click on 'Inbox.sbd' click on 'Bills.sbd' locate and delete : 'Gas' File - no extension 'Gas.msf' file example to locate 'Anne' In the profile mail account name click on 'Friends.sbd' folder locate and delete : 'Anne' File - no extension 'Anne.msf' file After deleteing the files as specified. * Close window - top right X * Start Thunderbird.