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. Since Outlook for Mac stores each items as an individual file, you can use Time Machine to back up your Outlook data.
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.
For more information about automatically archiving Outlook items by using Time Machine, see Automatically archive or back up Outlook items.
If you want, you can exclude Outlook data from your Time Machine backups. You can set this option in Time Machine preferences by adding the /Users/ username/Documents/Microsoft User Data/Office 2011 Identities/ folder to the list of items to be excluded from backups.