Need Help Converting an OST File to MBOX Format

I am facing a situation where I have an old OST file from my previous Outlook profile, but I no longer have access to the original Exchange account. I recently switched to a mail client that supports the MBOX format, and now I need to transfer all my emails from the OST file into MBOX. I have tried a few manual tricks, but nothing seems to work since OST files usually open only when linked with the original account. Can anyone guide me on the safest and most reliable way to convert an OST file to an MBOX file?