public ActionResult Index()
{
     var user = Session[“UserAccuont”];//从Session中获取当前登录用户的信息
     //send email
     var email = user.Email;
     …………
}

public ActionResult Index(UserAccount sessionUser)
{
     //send email
     var email = sessionUser.Email;
     …………
}

public class UserAccountModelBinder : IModelBinder
   {
       public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
       {
           if(controllerContext.HttpContext.Session["UserAccuont"] != null)
           {
               return controllerContext.HttpContext.Session["UserAccuont"];
           }
           return null;
       }
   }

protected void Application_Start()
{

    ………

    //凡是UserAccount类型的参数，都会使用UserAccountModelBinder来处理，也就是会从Session中取值

    ModelBinders.Binders.Add(typeof(UserAccount), new UserAccountModelBinder ());

}