18. Power to make rules as to transmission by post of postal articles

provide for the granting of receipts for, and the granting and obtaining of certificates of posting and delivery of postal articles, and the fees or sums to be paid, in addition to any other postage, for such receipts and certificates;

regulate covers, forms, dimensions, weights and enclosures of postal articles;

regulate the use of postal articles other than letters for making communications; and

prohibit the transmission by post of postal articles not specified in section 22 or lay down special conditions on which articles not specified in section 22 may be transmitted by post.