(6)Notwithstanding anything contained in the foregoing sub-rules, the authority issuing the notice or order may, if it thinks fit, order that the notice or order shall be served by sending a copy thereof, duly signed and sealed by registered post with acknowledgement due to the person on whom such notice or order is to be served and the posting of the notice or order shall be sufficient proof of the service of such notice or order on the person concerned.
