I am a letter carrier and I pick-up a lot of mail in ziplock bags, plastic wrap, and plastic newspaper bags when there is the threat of wet weather. I also see folks bring it wrapped in plastic to the P.O. during rainy days. What is suspicious is the fellows behavior, holding it away from his body, etc.
So I can still carry my mail in a Ziploc bag as long as I carry the bag in the "approved manner". Wonder where I can get the instructions for carrying a Ziploc bag.