except in accordance with this Act or unless authorised by a public postal licensee, wilfully retains or secretes or makes away with or keeps or detains or, when required by an employee of a public postal licensee, neglects or refuses to deliver up in the course of transmission by post any postal article or any mail bag containing any postal article; or
(b)
except in accordance with this Act or unless authorised by a public postal licensee, wilfully 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 guilty of an offence and shall be liable on conviction to a fine not exceeding $10,000 or to imprisonment for a term not exceeding 3 years or to both.
(2) Nothing in subsection (1)(b) shall apply to a person who does any act to which that subsection applies where he is a parent, or in the position of a parent or guardian, of the person to whom the letter is addressed and the addressee is a minor or his ward.