There are many methods that can be used to delete duplicate MBOX files, but I can suggest the best method for your problem. You can try the SameTools MBOX Duplicate Remover tool, which quickly finds duplicate items in the MBOX file and removes them without harming your original data. It will support all Windows OS versions like 11, 10, 8.1, 8, and 7 without downloading any other application. It has a simple, user-friendly interface for non-technical users and they can use it without technical skills. Users can try the free trial before buying this tool.