A technical method to remove duplicate emails from MBOX files is to use a specialized utility such as
SameTools MBOX Duplicate Remover. The utility automatically scans MBOX files and compares the emails, attachments, finds duplicate items and removes them. The purpose of the software is to discard only duplicated MBOX items while maintaining the original folder structure so that your data remains unaffected. It is easy to install on any version of Windows OS, like 11, 10, 8.1, 8, and 7. It also has a preview option to allow users to see the duplicates detected in MBOX before deletion. The tool has been designed with the end-user in mind, so both technically aware and novice users can facilitate smooth operation. Free trial versions are available for users.
Visit here:
http://www.sametools.com/duplicate/mbox/