def select(mailbox)
      synchronize do
        @responses.clear
        send_command("SELECT", mailbox)
      end
    end
Sends a SELECT command to select a +mailbox+ so that messages
in the +mailbox+ can be accessed.

After you have selected a mailbox, you may retrieve the
number of items in that mailbox from @responses["EXISTS"][-1],
and the number of recent messages from @responses["RECENT"][-1].
Note that these values can change if new messages arrive
during a session; see #add_response_handler() for a way of
detecting this event.

A Net::IMAP::NoResponseError is raised if the mailbox does not
exist or is for some reason non-selectable.