A notice authorised to be served on any person by section 87, 89(2) or 104(5) of this Act may be served on him by delivering it to him or by leaving it at his proper address or by sending it to him by post; and for the purposes of this section and section 26 of the Interpretation Act 1889 in its application to this section the proper address of any person shall be his latest address as known to the person serving the notice.