If you have an imap account then all emails are stored on the server and imap folder just show whatever you ahve on the server in those folders. When you select any folder, there is communication with the server to make sure you are seeing up to date information. When you select the 'Bin' folder, it chacks with server, if no emails are stored on server in Bin folder then it cannot display what does not exist. Do you have a settings which auto empties the 'Bin' when you exit Thunderbird? Right click on imap mail account name folder in Folder Pane and select 'SEttings' Select 'Server Settings' Message Storage: Is this selected : 'Empty Deleted fodler on Exit' If yes, then that explains why the 'Bin' is empty. However, it is also possible the server is auto emptying the Bin folder on server, so when you connect to server, it sees an empty Bin. Outlook.com automatically removes deleted emails from the trash after 30 days.