If you want to import or open MBOX data into Outlook, then you have to use a third-party solution. For the immediate solution of the MBOX to PST, I suggest the MailsDaddy MBOX to PST converter. With this tool, you can easily export multiple MBOX to PST format in few simple clicks. The software program is designed in very high quality, so it maintains folder hierarchy, rich text and attachments after export MBOX to PST format. You can see the preview after scanning the email with an attachment and you can also use the filter option to migrate some selected MBOX files. The tool is completely safe and reliable, so I prefer this device.