Outlook 2011 for Mac data can be backed up in a number of different manual and automated methods.
Mac users can use Apple's Time Machine to backup their data to an attached external drive or another disk partition (Apple does not support network drives).
This techinique has the advantage of storing your Outlook 2011 for Mac data into a single file for safe keeping or transfer to another Mac.
To make a local file archive of your Outlook 2011 for Mac information:
If one or more email folders are extremely important, you can drag all the messages of a particular folder from the Outlook 2011 for Mac folder list (left side) to a folder on the Mac's desktop. You will need to create a folder of the same name on the desktop using the Finder. Select the desired folder in Outlook 2011 for Mac in the folder list. Select all the messages in the folder using Command-A (Edit menu, Select All) and drag the messages to the folder on the desktop to make copies.
The disadvantage to this technique is that the folder hierarchy is not retained in the backed up files and it does involve using the Finder to create folders with the same name to organize the messages.
A quick backup method to back up all your Outlook 2011 for Mac data is to drag the folder "Microsoft User Data" from your "Documents" folder to an external drive.