Check if mail already exist when register new user
<p>I need some feedback on this code:</p>

<pre><code>protected void RegisterUser_CreatingUser(object sender, LoginCancelEventArgs e)
{
    var mail = RegisterUser.Email.ToString();
    if (mail == "already existing mail")
    {
        e.Cancel = true;
    }
}
</code></pre>

<p>I want stop new users to register with an email that is already registered. What is the best way to go??</p>
