If you are using a PST as a mail store, you would simply need to make a copy of the PST when outlook is closed. The default path is C:\Users\Username\Document\Outlook Files\Outlook.pst. Several different methods are available to make scheduled copies, but Microsoft's SyncToy is nice and easy. Simply set up synchronization to run during a period when your Outlook is closed, and have it move the PST to your backup location.
