No, I am afraid if there is any free solution to this problem. Outlook and Mac mail, though immensely popular on Mac, fail to keep similar database type. While Outlook manages its mails in OLM format, Mac mail saves the mails in MBOX format. None of the two import the other.
Along with the emails, its necessary that the converter you opt for shall be able to convert the contacts and the calendars. Moreover, the mail folder hierarchy needs to be restored safely at the other end.
In my knowledge, OLM Converter Pro is the only application that offers services to this extent.
A brilliant tool that has a keen eye for every aspect.