Time Machine is a backup software application included with the Apple OS X operating system. To use it, you'll need an external storage system, such as an external hard drive. Turn Time Machine on and it automatically makes copies of the files on your computer on a regular basis. If you lose or damage a file, you can use Time Machine to browse through the backups to recover a copy of the file.
Turn Time Machine on to back up your Outlook items
On the Apple menu, click System Preferences, and then click Time Machine.
In the Time Machine dialog box, switch Time Machine to On, and then click Select Backup Disk.
Select the location where you want to back up your files, and then click Use Disk.
Your files will now back up daily.
Note: The first time you open Outlook after restoring a Time Machine backup, Outlook rebuilds its database to accommodate the restored items. If you have a large database, rebuilding the database might take a while.