When I came into the same problem, I agreed to use the
SysInspire Thunderbird to Outlook Converter . This tool is one of the best I've ever used because it allows me to copy thousands of MBOX files in a single operation. The best part of this app is that it works well on Windows OS 10. It allows you to save MBOX files as Outlook PST, MSG, PDF, EML, HTML, and other formats.
Here is the solution to Extract Emails from MBOX File