How to Create E-Mail Messages in Outlook 2013
Click the Check Names button in the New Message form’s Ribbon (or press Ctrl+K).
If you haven’t memorized the exact e-mail address of everyone you know (gasp!), the Check Names feature lets you enter a part of an address and then looks up the exact address in your Address Book so that you don’t have to be bothered. Double-check what Check Names enters; sometimes it automatically enters the wrong address, which can yield embarrassing results if you don’t realize it and send the message.