Whoever fraudulently retains, or willfully secretes or makes away with, or keeps or detains, or when required by an officer of the Post Office, neglects or refuses to deliver up, any postal article in course of transmission by post which ought to have been delivered to any other person, or a mail bag containing a postal article, shall be punishable with imprisonment for a term which may extend to two years, and shall also be punishable with fine.