Post man and parcel delivery people wake up my baby

I have two problems.

One is very loud letter box through the door that makes flap noises, and delivery people knocking on my door like there is no tomorrow.

The second one, I guess I can rectify with a note or sticker on the door?

But letters are a bit more tricky. Shall I get a plastic box outside? Or maybe I shall get a wall mounted box, or there are quiter flaps? Really open for your experience and ideas :)