Whoever steals, purloins, or embezzles any property used by the Postal Service, or appropriates any such property to his own or any other than its proper use, or conveys away any such property to the hindrance or detriment of the public service, shall be fined under this title or imprisoned not more than three years, or both; but if the value of such property does not exceed $1,000, he shall be fined under this title or imprisoned not more than one year, or both.