Import and export of goods by post: 

In the case of goods imported by post the agency for the carriage of goods is the Government of India be it through sea, air or land. The control of the Customs Department is only on goods, whether imported or exported

(i) on which there is a duty; and

(ii) which are subject to prohibition or restriction under the Customs Act or any other law for the time being in force.

The customs have no concern over other goods or other mail.