Ok, I have been suck on it for hours. I thought net/imap.rb with ruby 1.9 supported the idle command, but not yet.

Can anyone help me in implementing that? From here, I though this would work:

class Net::IMAP
  def idle
    cmd = "IDLE"
    synchronize do
      tag = generate_tag
      put_string(tag + " " + cmd)
      put_string(CRLF)
    end
  end

  def done
    cmd = "DONE"
    synchronize do
      put_string(cmd)
      put_string(CRLF)
    end
  end
end

But imap.idle with that just return nil.