Install Mozilla Thunderbird:
Download and install Mozilla Thunderbird on your computer.
Configure Thunderbird:
Open Thunderbird and set up a new email account.
Install "OST Viewer" Add-on:
Install an add-on called "OST Viewer" in Thunderbird. This add-on allows you to view and import OST files.
Import OST into Thunderbird:
Open Thunderbird and go to "Tools" > "ImportExportTools" > "Import OST file."
Choose the OST file you want to convert.
Export to MBOX:
Once the OST file is imported into Thunderbird, you can use Thunderbird's export feature to save emails as MBOX files.
Regards,
Peter