How do you behave with a person at your doorstep? Do you scare him off or greet him? You don't beat him away, do you? Your puppy learns from this and also greets the person at the doorstep. He learns from his master. He learns that not everyone at your door is an intruder.
You have a well-behaved puppy and you should encourage this. You don't want your dog to attack anyone at your doorstep.
Don't tie him. Dogs that are confined usually feel very unsecured and are likely to attack their owners or anyone.
Remember, he is an animal not a loaded gun.