This tutorial will show you how to automatically move mail OUT of your live Exchange mailbox, and place it on your local computers harddrive. As always, make sure you have a backup plan for your computer in the event of a system failure or theft. Once this mail is moved out of the Exchange mailbox system, you will be the only one who has a copy.
Outlook 2011 for Mac is backup friendly, including Apple's TimeMachine backup application. With Entourage, mail was stored on your computer in a single database that grew and grew. The only way to make a backup was to copy the whole thing over to a backup drive periodically. Outlook 2011 has a file structure that allows for incremental backups, which means you only have to backup the most recently changed files, and not the whole database, making backups quicker.
Step 1) In Outlook 2011 for Mac, from the Tools menu, select Rules.
Step 2) Select Exchange in the rules window, and click the "+" sign to add a new rule.
Step 3) Name the Rule: 180 Day Auto Archive, or what ever is suitable.

Step 4) Under the "If" section, define the criterion as: "Date Recieved" + "is greater than or equal to" + "180" ... days old
Step 5) Under the "Then" section, define the action as: "Move message" + "inbox on My Computer"
The location "My Computer" is your local computers copy. If you pull down in that menu, you'll see that you can specify another location if necessary.
Step 6) Finally, Click "Ok", making sure that the Enabled button is selected
If you would like to apply this rule to your current mailbox, then...

Step 7) From the Message menu, select Rules, then the rule you would like to process.
This process may take some time to run initially, depending on how much mail you have in your inbox.