I want to suggest the MBOX Duplicate Remover Tool if you want to
delete large-size MBOX duplicate files. This solution is available on the internet and is the best approach to remove duplicate emails from MBOX files. It is an error-free solution that allows users to delete several duplicate files at once while keeping all data, and it can also connect directly to Thunderbird to remove duplicate mailboxes. This application accepts MBOX files from a wide range of email clients, including Thunderbird, Apple Mail, Entourage, Eudora, Opera Mail, and others, without the need to install Thunderbird. I used this utility on my large duplicate folders and had the best luck removing duplicate emails from MBOX files. Users can download it without any technical skills, as it provides a basic graphic interface so users can connect with its features without having technical errors.