I can strongly recommend you to use Stellar Converter for MBOX because, in the past, I wanted to convert my Apple mail MBOX file to Office 365 and tried many third-party tools. Stellar Converter for MBOX is perfectly fit for my requirement and resolves my problem. Some of the best features which I like the most and make different from other tools available on the internet such as able to convert single as well as multiple files, you can save converted PST file to new or existing PST file, a preview of email before conversion, support save converted email to Office 365, RTF, PDF, and HTML, support 15+ email clients, filter-based conversion and many more. Also, you can see your conversion process log report. You can check out their official product page for more information.