def idle(&response_handler)
      raise LocalJumpError, "no block given" unless response_handler

      response = nil

      synchronize do
        tag = Thread.current[:net_imap_tag] = generate_tag
        put_string("#{tag} IDLE#{CRLF}")

        begin
          add_response_handler(response_handler)
          @idle_done_cond = new_cond
          @idle_done_cond.wait
          @idle_done_cond = nil
          if @receiver_thread_terminating
            raise Net::IMAP::Error, "connection closed"
          end
        ensure
          unless @receiver_thread_terminating
            remove_response_handler(response_handler)
            put_string("DONE#{CRLF}")
            response = get_tagged_response(tag, "IDLE")
          end
        end
      end

      return response
    end
Sends an IDLE command that waits for notifications of new or expunged
messages.  Yields responses from the server during the IDLE.

Use #idle_done() to leave IDLE.