Secure solution for Apple Mail export Mailbox to Outlook Mac

How to export Apple Mail to Outlook 2011 safely? I’ve very important email content in my Mailbox related to business deals and I want to transfer it to Outlook 2011, as I have been switching to Outlook Mac, in future. Is there any simplified approach for Apple Mail export Mailbox to OLM procedure? Please avail suggestions for effectual services.

Thanks in advance, for assistance!