You can remove duplicate emails across multiple Outlook folders then use a best solution like SameTools PST Duplicate Remover. It can automatically search duplicate items in the Outlook folders and remove them within a few simple steps. The software has an easy interface for non-technical users, and they can use it. The tool does not need to install any other application for removing multiple duplicate items in the Outlook folders; it is enough for it. The software runs on all Windows OS versions like 11, 10, 8.1, 8, and 7. It provides a free trial you can use it before buying this tool, and after removing duplicates from Outlook folders it will give a preview and the results.