I catch post request from 3rd-side static page (generated by Adobe Muse) and handle it with MVC action.
Change void to ActionResult.
[HttpPost]
public ActionResult Index(EmailModel email)
And don't forget verifying AntiForgeryToken from your view and action.
// to your form in view
@Html.AntiForgeryToken()
// ------------
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Index(EmailModel email)