You can cancel your Yahoo! Mail Personal Address service anytime. Here's how:
If you choose to cancel, we'll disable your email service and not renew your subscription. We regret that we'll be unable to refund you for the domain that you registered. However, you'll continue to own the domain name for the remainder of your registration term.
Note: If you want to cancel your entire Yahoo! ID and/or Yahoo! Mail account, please submit a request.