I had to make a formal complaint to Royal Mail because the postie wouldn't knock or ring the doorbell, posting a slip to save them time!
It happened at least 10 times.
It's a 10 mile trip each time to the sorting office for us.
I call them Royal Fail now.
It's because the postie doesn't want to carry your parcel. I've caught them a couple of times putting a card though the door, and when asking for the parcel they admit it's back at the sorting office, or if you're lucky it'll be on the van with his mate doing the local parcel deliveries before picking the postie up again.