Section 46B(1) in The Indian Post Office Rules, 1933
(1)No article sent in envelopes which are wholly transparent shall be transmitted by post. Articles in envelopes with a transparent panel may, however, be transmitted by post provided they conform to the following conditions:-(a)The transparent panel shall be parallel to the greatest dimension so that the address of the addressee appears on the same direction and the application of the date-stamp is not interfered with.(b)The address shall be clearly legible through the panel and no other communication shall be visible through the panel so as to affect the clarity of the address.
