I utilised the MBOX Duplicate Remover Tool, which has the ability to delete MBOX duplicates in bulk, to fix duplication when I opened several MBOX files that I received from my friend in Thunderbird. It just resolves all mailbox duplicates in a single round, without causing any file damage. I so suggest using this application. The demo version is available for download right now. Read More :- https://www.softakensoftware.com/mbox-file-duplicate-remover.html