Rails Exception Notifier does not send mail on 404

I could request a page that does not exists and I would suppose a 404 would be send, but with the configuration below I receive mails for other errors but not for 404.

What could I do?

Rails.application.config.middleware.use ExceptionNotification::Rack,
  :ignore_crawlers => %w{Googlebot bingbot},
  :ignore_cascade_pass=>false,
  :email => {
    :email_prefix => "[Exception] ",
    :sender_address => %{" Production" <mail@example.com>},
    :exception_recipients => %w{mail2@example.com}
  }