I have 7.1 at work. Under Notifications it reads, "When new messages arrive: under which there are 2 check boxes. The first one reads, "Show an alert." The second one reads, "Play a sound." Under the second one and slightly indented are 2 radio buttons. The first reads, "System New Mail Sound." The second one reads, "Custom .wav file." When you select that one, it enables a box and a browse and preview button so you can select your own sound.