Can email field be made unique while creating new user using createuserwizard in asp.net.

Hi Guys,
I am using ASP.net createuserwizard to create new users(User regrestration) in my web site.The problem which I have is :
lets imagine that  if the same user registers more than one time with different user id'b but same email address the asp.net createuserwizard will not restrict such regrestrations,since he is using different user id,s to register every single time.
In this scenario I want to implement Forgot Password or user name functionality where in I am trying to recover the user name or password of the user based on the email(id which he gave during regrestration process) id which he has to provide as input.After providing the input i am fetching the security question of the user from the database for that particular email id. As in this case we have the same email id's for different users(as the same person has regrestered with different user id's but same email id) my question here is how do i get the right security que ...