.Net Membership Provider not catching email duplications

Question

I am relatively new to .Net/MVC3, and am working on a C#, MVC3, EF4 application that makes use of the default membership provider. From my reading, it should automatically catch duplicate emails, but it does not seem to do so, and I'm not certain why. What I really need to figure out is where to look to see if the right pieces are in place, and for the reason(s) why it might not do that validation check (it seems to do most/all of the others, like duplicate user names, or invalid password formats, etc. with only duplicate email not getting caught.)

Customizations include adding new users to a specific role, and redirecting to a 'first time' welcome page.

Here is the code:

    // POST: /Account/Register

    [HttpPost]
    public ActionResult Register(RegisterModel model)
    {
        if (ModelState.IsValid)
        {
            // Attempt to register the user
            MembershipCreateStatus createStatus;
            Membership.CreateUser(model.UserName, model.Password, model.Email, null, null, true, null, out createStatus);

            if (createStatus == MembershipCreateStatus.Success)
            {
                FormsAuthentication.SetAuthCookie(model.UserName, false /* createPersistentCookie */);
                Roles.AddUserToRole(model.UserName, "Registered");
                //return RedirectToAction("Index", "Home");
                return RedirectToAction("Acceptance", "Account");
            }
            else
            {
                ModelState.AddModelError("", ErrorCodeToString(createStatus));
            }
        }

        // If we got this far, something failed, redisplay form
        return View(model);
    }

Here are the (untouched) validation methods:

 #region Status Codes
    private static string ErrorCodeToString(MembershipCreateStatus createStatus)
    {
        // See http://go.microsoft.com/fwlink/?LinkID=177550 for
        // a full list of status codes.
        switch (createStatus)
        {
            case MembershipCreateStatus.DuplicateUserName:
                return "User name already exists. Please enter a different user name.";

            case MembershipCreateStatus.DuplicateEmail:
                return "A user name for that e-mail address already exists. Please enter a different e-mail address.";

etc.

Answer 1

By default, only usernames must be unique. If you want unique email addresses as well, then you must set that in the Web.config entry for the MembershipProvider.

something like

<membership>
  <providers>
    <add name="AspNetSqlMembershipProvider" [...] requiresUniqueEmail="true" [...] />
  </providers>
</membership>