In my opinion, you can remove duplicate emails from large MBOX files then you should try the best tool becouse manuallly removing is too risky and too time-consuming. I can suggest a perfect tool for it, try the Gaintools MBOX Duplicate Remover which can scan MBOX files finds duplicate items and remove them without facing any issues. The software is compatible with all versions of Windows OS like 11, 10, 8.1, 8, and 7. There is no need to download any other application. Non-technical users can use it without technical skills becouse it has a simple interface. It will provide a free trial so you can try it before buying the full edition.

Visit here: https://www.gaintools.com/mbox/duplicate/