未找到视图“错误”或其主控 - web.config未指定错误视图

Background: On a public facing ASP.NET MVC4 application, sometimes I receive inbound requests to a bad URL. The referrer is from outside so my app which is out of my control (I'm not generating the bad URL in my app). So MVC correctly raises an exception AND the user sees the custom error page. The global.asax is coded to email errors to me.Background: On a public facing ASP.NET MVC4 app