One our former mail ladies used to dish out dog treats, she really liked our dog and would give her multiple treats every day. I couldn't figure out why the dog was getting fat until I saw her toss treats out down the driveway as she was driving away. A friendly conversation later she cut her back to one a day, needless to say the dog was still very happy to see her each day.
Our current mail lady does not give treats but our current dog likes to greet her if he's out. She gives him a pat and tells him to go to the house, which he does. The other delivery folks do occasionally give him cookies, he's really happy to see them.
He's a golden retriever so while a bit noisy at times, he is not very scary.