The Trash will empty under specific circumstances. '''1. The 'TRash' folder has a retention policy set to delete.''' * Right click on TRash folder and select 'Properties'. * Select 'Retention Policy' tab * Select Use my account settings and Don't delete any messages' to prevent deletion by Thunderbird. * click on 'OK' '''2. Trash folder has an Account setting to empty on exiting Thunderbird.''' * Account SEttings > Server Settings for the account * Bottom right under 'Message Storage' * Uncheck the checkbox 'Empty Deleted folder on Exit' to prevent deletion by Thunderbird. '''3. Server uses an auto delete policy for emails put in TRash after a specific period.''' This setting will only effect Imap mail accounts. So you may select an imap TRash folder and it synchronises with server to show what is on server and if server has deleted emails then they do not exist so cannot be displayed. Various servers have their own policy on what to do with emails which have been put into Trash because the emails in Trash are unwanted. It is normal to have emails sit in the Trash for a short period just in case they were deleted in error and need to be retrieved. Here are some examples: Gmail will empty emails from Trash every 30 days approx. https://support.google.com/mail/answer/7401?hl=en&co=GENIE.Platform%3DDesktop the Yahoo server 'Trash' folder should get auto emptied by the server every 7 days. https://help.yahoo.com/kb/trash-spam-folders-regularly-emptied-sln3518.html Xfinity server auto deletes every 14 days. https://www.xfinity.com/support/articles/set-email-deletion-settings