Time Machine is an application included with Mac OS X that backs up your computer. If you turn on Time Machine, it automatically makes copies of every file on your computer on a regular basis. If any file gets damaged or lost, you can use Time Machine to browse through the backups and recover the copy of the file.
Do any of the following:
Turn on Time Machine to automatically archive Outlook items
Since Outlook for Mac stores each items as an individual file, you can use Time Machine to back up your Outlook data.
On the Dock, click the Time Machine button, and then click Set Up Time Machine
In the Time Machine dialog box, click Select Backup Disk.
Select the location where you want to back up your files, and then click Use for Backup.
Your files will now back up daily.
Note: The first time that you open Outlook after restoring a Time Machine backup, Outlook rebuilds its database to accommodate the restored items. If you have a very large database, rebuilding the database might take a long time.
Stop automatically archiving Outlook items
On the Apple menu, click System Preferences.
Click Time Machine, and then click Options.
Click Add, and select the /Users/ username/Documents/Microsoft User Data/Office 2011 Identities/ folder.