Microsoft Outlook has a directory, called the "Global Address List" that includes all active faculty, staff and students.
If you know the first and last name of the person you would like to address the message to, you can enter it in the To:, CC: or BCC: field, and hit Control+K or click the "Check Names" button in the home tab on the ribbon. This will cause Outlook to check the name against the directory. If there is a match, Outlook will underline the name; if there are multiple people with the same name, you will receive a pop up window listing all of the people with the same name, and you can choose the correct person based on other information, such as their title, e-mail address, office address, or phone number.
If you want to search by last name only, enter the last name in the To:. CC: or BCC: field, and hit Control+K or click the "Check names button. This will display a dialog with all of the people with that last name. You can then select the correct person based on their first name, title, e-mail address, office address, phone number, etc.
If you would like to browse the directory, you can open the directory by clicking the "To:", "CC:" or BCC:" button on a new e-mail message, or click the "Address Book" icon under the home tab of your Outlook ribbon. This will display all active faculty, staff and students in first name, last name format. You can search by first name, or, if you would like to search by last name, change the search type at the top from "Name only" to "More Columns". Alternatively, you can click on "Advanced Find" and search by first name, last name, e-mail address, department, etc.
Note: Once you send an e-mail to a particular person/address, this address will be stored in your recent contacts, and the next time you address a message and start typing in the name, type-ahead will activate and display a list of addresses to choose from.