Bending Pixels, Outlook can import .mbox files, but Mail creates a non standard type of .mbox file. You have to convert these to standard .mbox THEN you can import. However unlike Mail that imports a folder of .mbox files, Outlook imports one file at a time.
Emailchemy converts Apple MBOX to .mbox.
http://www.weirdkid.com/products/emailchemy/
Your best option to move your messages is to use IMAP account.
MacAndrew07, if you have POP accounts, your data stored under "On My Computer" folders is not safe in Outlook. Rebuilding often fails and recovering from Time Machine requires you to rebuild because the database file is not backed up to Time Machine.
Outlook for Mac is a version 1 product where Outlook for Windows is a mature product. Expecting them to have the same features and stability is a bad assumption.
To get your contacts in Snow Leopard Address Book to Outlook Address Book still works using Sync Services. Open Outlook Prefs and make your selections under Sync Services. BACKUP data in both devices first.
Sync Basics
Outlook does not support CalDAV or CardDAV so sync between Outlook and Apple applications are slowly going away. CalDAV & CardDAV are protocols used by*Apple, Google, Yahoo and others to sync contacts and calendars.
Apple has deprecated Sync Services in Mountain Lion and it no longer works reliably.
- You can no longer sync with an iPhone or iPad via iTunes. You can only sync with an iPhone or iPad via a cloud-based service like iCloud or Google.
- You can no longer sync local calendars with OS X Calendar (formerly iCal). You can, however, continue to sync calendars hosted on a cloud-based service like iCloud or Google with OS X Calendar.
- You can no longer sync with any third-party apps running on your Mac that use Sync Services, like Entourage or Outlook.