public void ErrorMail_Filtering(object sender, ExceptionFilterEventArgs args)
{
	Filter404Errors(args);
}

private void Filter404Errors(ExceptionFilterEventArgs args)
{
	if (args.Exception.GetBaseException() is HttpException)
	{
		var httpException = args.Exception.GetBaseException() as HttpException;
		if (httpException != null && httpException.GetHttpCode() == 404)
			args.Dismiss();
	}
}