Section 26(2) in The Indian Post Office Rules, 1933
(2)Samples of seeds, drugs and other articles which cannot be sent in unfastened or removable envelopes may sent enclosed in boxes or bags, provided that they are fastened in such a way that they can be easily opened, they may also be sent in airtight cases, when necessary, provided that the nature of the contents is certified on the cover under the full signature and address of the sender.
