If you have access to the gamertag on your Xbox 360 console, please go to your Dashboard > Settings > Account > 3rd Tab (Account Information) > Account Security > Look to the right, and you'll see the e-mail you should be using to sign into Xbox.com to get
your gamertag to show up.
If you don't have the means to do that then I would suggest that you Chat with Microsoft Support or Request a Call. You can do either option by going to this page here and clicking
on Billing and Memberships, under Microsoft Account click Forgot Microsoft Account Username. You'll need to be able to provide the agent with the information on the account before they are able to give you the e-mail associated with the account. If you're
not able to provide them with the information they are asking then they will not be able to assist you with your inquiry.
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