How to gain control over an account?

Im trying to sell this account I've had for a while.

I have the password, recoveries, and well, that's about it...How can I get the email registered?

 

There is no 100% way to "own" an account unless you are the account's creator. You cannot 100% transfer control of an account to someone else, even if they have email/recoveries/password, the original owner at any time can take the account back.

If you want to set an email, login to the game site, go to account settings, and then click email registration