Thunderbird add-on for duplicate message removal.
This extension is specifically designed to make removing duplicate messages a breeze. Simply select the folder you want to check for duplicates, and the extension will display a dialog allowing you to choose which messages to keep and which to delete. If you prefer not to see the dialog, you can opt to have the superfluous messages deleted automatically without intervention.
With the help of this extension, you'll be able to easily search for and remove duplicate messages, which are often referred to as 'dupes.' This can save you a significant amount of time and effort, and make it easier to manage your email effectively. Overall, if you're looking for an efficient and reliable way to rid your Thunderbird mailbox of duplicate messages, the Remove Duplicate Messages (Alternate) extension is definitely worth considering.