The message/pop up has nothing to do with emails you have put into the 'Trash'. The message does not mean 'Empty the Trash'. When you move emails from one folder to another, the email is still in the original folder, but you cannot see it because it is hidden and marked with a type of flag to say delete/remove this old email when compacting file. That 'moved' email maybe something you moved from Inbox to the Trash or Junk or move to another folder for storage like 'Family'. But the Inbox still has a hidden marked as deleted copy. It is these hidden marked as deleted copies that the pop up is talking about. They need to be removed, so file can be cleaned up. It is part of a basic maintenance to help keep a healthy Thunderbird. If your Options settings have reached a threshold you will get the pop up and the best advise is to finish what you are doing and compact the folders. More info on compacting: https://support.mozilla.org/en-US/kb/compacting-folders Please note: The wording in this pop up has caused a lot of confusion. I reported a bug and it was discussed. The wording has been improved and in version 91 it will be implemented. So you may find some of the information at the link to be showing the new changes; not current in version 78*

Thanks you very much for your help