Whoever, not being an officer of the Post Office, willfully and maliciously, with intent to injure any person, either opens or causes to be opened any letter which ought to have been delivered, or does any act whereby the due delivery of a letter to any person is prevented or impeded, shall be punishable with imprisonment for a term which may extend to six months, or with fine which may extend to five hundred rupees, or with both:
     Provided that nothing in this section shall apply to a person who does any act to which the section applies, if he is a parent, or in the position of a parent or guardian, of the addressee, and the addressee is a minor or a ward.