A person who wilfully opens or reads, or has opened and read, a sealed letter not addressed to the person, without authority to do so by the writer or by the person to whom it is addressed, or who wilfully, without the same authority, publishes a letter or portion of it, knowing it to have been opened without the authority of the writer or addressee, upon conviction, is punishable by imprisonment in jail not less than one month nor more than one year, or by a fine of not less than $50 nor more than $500. This section does not extend to or include an act made punishable by a law of the federal government.