Web API 2 not working (404)

For me routing attributes were not working with WebAPI because I had the URL Rewrite module installed in my web.config. Somehow the global routing templates were working with that in place but not the routing attributes above each web method. I removed the <rewrite> section from within the <system.webServer> section in web.config and the routing attributes started working.

please update your global.asax like here:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    GlobalConfiguration.Configure(WebApiConfig.Register);
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);

}

and change [Route("~/api/sendemail")] to [Route("/api/sendemail")]