One of the first things that is required when you start your new Xbox 360 is to create a profile. This profile, called a gamertag, must be linked to an e-mail address that will be used to create your "Windows Live ID." If you have forgotten the email address you have used, the only way to find out the email address is through your Xbox 360 console.
Turn on your Xbox 360.
Press the "Guide" button on your controller. Select "Sign In." Select the profile (gamertag) you wish to sign in under and press "A."
Press the "Guide" button. Press the joystick to the right twice to reach the "Settings" window. Select "Account Management." Press "A."
Select "Windows Live ID" and press the "A" button. The email linked to your gamertag will be displayed under the "Windows Live ID" window on the right-hand side of the screen.