18.—(1) Any document required or authorised by these Rules to be sent or delivered to any person shall be duly sent or delivered to that person:—
(a)if it is sent to him at his proper address by post;
(b)if it is sent to him at that address by facsimile or other similar means which produce a document containing a text of the communication, in which event the document shall be regarded as sent when it is received in a legible form;
(c)if it is delivered to him or left at his proper address.
(2) The proper address for the Pensions Ombudsman is the address of the office of the Pensions Ombudsman.
(3) The proper address of any other person to whom any such document is to be sent or delivered shall be the address given by that person or, if none, the last known address of that person or, in the case of an incorporated company or body, the registered or principal office of that company or body.