You can remove duplicate emails across multiple Outlook folders, then I can suggest a perfect solution becouse I'm also using it. You can try the TrustVare Outlook Duplicate Remover, which quickly finds duplicate items in the Outlook files like email, contacts, notes, tasks, calendar, etc, and removes them without affecting original data. The software is simple becouse it has an user friendly interface for non-technical users and they can use it. The software works with all Windows OS versions like 11, 10, 8.1, 8, and 7, without downloading MS Outlook. It can provide a free trial before purchasing this tool and it will give you a preview option before removing duplicate Outlook items.