To make the Global Address List the default list in your Address Book (this example is from Outlook 2010):
- Open the Address Book from the Home tab on Outlook's menu ribbon (not by opening an email and clicking the To button!). It will be near the right end of the ribbon.
- Find Tools on the Address Book menu bar, and select Options
- At the bottom of Addressing Options, select Global Address List from the drop-down list under "When opening the address book, show this address list first:" and click OK.