shabbat - Putting something in the mailbox that will be picked up on Shabbos or Yom Tov

Are you allowed to put an envelope in your personal mailbox that will be picked up on Shabbos or Yom Tov?

Answer

The Sanctity of Shabbos by Rabbi S. B. Cohen pg. 107 writes: "One is also permitted to place mail in his personal mailbox on Friday. (If one knows, however, that his mailman is Jewish, this is prohibited.)" Amongst his sources is אגרות משה או"ח ח"ג [סוף] סי' מ"ו.