When you click on the Search field at the top of Outlook's message list, the Ribbon displays a new tab labeled Search Tools.
In the Search Tools tab, find the icon labeled Search Tools (it's the second icon from the right), click the down arrow and choose Advanced Find to open a dialog that lets you fine-tune your search.
While this tab is open, you might also want to click on the Search Tools icon, then choose Search Options to add further controls to your Outlook searching.
The same Search Options dialog is also available from anywhere in Outlook by using the File menu, then Options, then scrolling down to Search.
View the outlook 2010 screenshot below.