When you sign up for services with AT&T phone or Internet services, you are automatically given an @att.net email address. This is how AT&T communicates important news and account status to you, such as billing information and rate plan offers. Not everyone would like to use their AT&T email account, though, and it is possible for it to be closed without canceling your service with AT&T or pretending the account doesn't exist. Since AT&T uses Yahoo! for their email accounts, the deletion process is the same as it is with Yahoo!.
Open the att.net home page. If you are not already logged in, click the "Log In" button in the top-right corner and sign in to your account.
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Open the following link: https://edit.yahoo.com/config/delete_user. This will lead you to the account termination page. Confirm your identity by typing in your password.
Another page will appear describing what you will lose when you terminate your account. If you still wish to proceed, click on the "Terminate this Account" button.