America Online, Inc. (plaintiff) owned three trademarks in connection with its Internet service: “Buddy List,” “You Have Mail,” and “IM.” AOL’s Buddy List was a subscriber’s list of contacts who also used the company’s real-time messaging service, “instant messaging,” or “IM.” AOL obtained a service mark registration for “Buddy List” from the United States Patent and Trademark Office (PTO). With its email service, AOL alerted subscribers that they had new mail by displaying the words “You Have Mail.” AT&T Corporation (defendant) was a competitor of AOL, and used the terms “Buddy List”, “You have Mail!”, and “I M Here.” in connection with its Internet service. AOL sued AT&T for trademark infringement. AT&T presented evidence that the phrase “You Have Mail” was used to denote the existence of new mail well before AOL even came into existence. AOL presented evidence that the public associates “You Have Mail” with AOL. The district court granted AT&T summary judgment on the ground that the service marks were generic. AOL appealed.