Whoever, being an officer of the Post Office,--
         (a) fraudulently puts any wrong official mark on a postal article, or
         (b) fraudulently alters, removes or causes to disappear an official mark which is on a postal article, or
         (c) being entrusted with the delivery of any postal article, knowingly demands or receives any sum of money in respect of the postage thereof which is not chargeable under this Act,
shall be punishable with imprisonment for a term which may extend to two years, and shall also be punishable with fine.