If you have an MBOX file and you are willing to open it in Outlook. Then there is no direct solution for this. First of all, you have to export your MBOX file in PST format. For your exporting needs, SysTools has developed an advanced MBOX to PST Converter Tool. It is quite easy to use this utility, just follow the steps:

1. Download SysTools Software from the Official webpage: https://www.systoolsgroup.com/mbox-to-outlook-converter.html
2. Install and Add The MBOX File into Software Panel
3. Preview Entire Data of MBOX and Verify
   
4. Select PST Radio Button and Hit Export
5. After Completing Conversion, You have a PST file
6. launch the Microsoft Outlook and hit Import/Export
7. Select the PST file and import it

Now you can easily access all the mails in Outlook and we can say that SysTools utility helped you to import MBOX file in Outlook account.