Importing is always considered as a task rather it is related to anything. One does not exactly knows what to do and how it is to be done until and unless one have a perfect knowledge to do so. Therefore converting your mail database from MBOX or EML is an humongous task again as one is aware of the conversion process manually and which is the best converter to do so is also a big point to think.
To easier your importing task the Mail Passport Lite is the solution. It import MBOX to Outlook for PST files and lead to successful migration of your mail database. It covers each and every single unit in your database for the conversion rather it is mails, contacts, calendars, attachment, etc. It is a converter tool supported by Windows operating system but conversion can be done for both Mac and Windows as both supports PST files for Outlook.
It also import EML to Outlook fore PST files which make it a two in one converter tool for conversion of mail database. It simply means you can convert both MBOX and EML file with this single converter tool. This tool comes with an easy to use interface and a free trial version to allow you to experience migration using this converter tool as it converts 10 file per folder.
For more details: http://www.mailpassportlite.com