def setquota(mailbox, quota)
      if quota.nil?
        data = '()'
      else
        data = '(STORAGE ' + quota.to_s + ')'
      end
      send_command("SETQUOTA", mailbox, RawData.new(data))
    end
Sends a SETQUOTA command along with the specified +mailbox+ and
+quota+.  If +quota+ is nil, then quota will be unset for that
mailbox.  Typically one needs to be logged in as server admin
for this to work.  The IMAP quota commands are described in
[RFC-2087].