The Microsoft Exchange Global Address List is a list of all users and their respective email addresses within an Exchange Server organization that
uses Microsoft Outlook for email. This list shows when you are sending an email and you click the To or CC buttons on outlook.
To change the default global address list on outlook 2010, follow the instruction bellow.
1. Open outlook and click the Home if you are not there already.
2. Click the Address Book icon on the top right corner of outlook
3. On the Menu, select Tools -> Options
4. Choose Custom and move the default address book or the address book you want to show up on start
5. Under the When opening the address book, show the address list first selection, choose the correct address list.