Can I get something back if I accidentally dropped it in the mailbox?

yeah you could get it back if it didn't have an address on it, but I don't know if you can get it back because it doesn't have your full name or what not,but if you go to the post office and said that you slipped a letter in the mail box that wasn't intended to be sent anywhere you'll probably be good because: 1)there's no address, 2) it wasn't like it was going anywhere to someone else; so yeah just go to the post office and try to claim it unless they already threw it away or something.