NOTE: This article applies to Outlook 2011 on an Apple Mac. If you're using Outlook 2007 or 2010 on a Windows PC, please refer instead to FAQ 2259.
When you delete items such as emails and contacts list entries they are moved to your Deleted Items folder. When you empty the Deleted Items folder, the items are no longer accessible to Outlook 2011, but remain potentially recoverable for 28 days.
To recover them you will need to login to OWA (Outlook Web App) at:
Once logged in, ctrl-click (or right-click) on the Deleted Items folder and select Recover Deleted Items:
This will open the Recover Deleted Items window. To recover a message ctrl-click (or right-click) on it, click Recover and then select the folder into which you wish the recovered message placed: