Email file migration (From outlook 2011 to mac mail)

Hello every one,
I am here with a problem of mail migration. Since one month month I have been trying to migrate my emails from outlook 2011 over to apple mail. But that seems a tough job to be done. The import function in apple mail does not contain outlook 2011 in the import from menu and I have spent hours for searching solutions for this migration online and have not found a perfect solution yet. Please guide me with a perfect method or solution that can help me migrate all my mails from outlook 2011 to apple mail.

Currently I am using mac book pro having mac osx 10.8.3. I have thousands of mails to be migrated.
I hope to get helpful solutions.
Thanks