Always found this problem quite interesting. In the UK, parcels are rarely if ever left on the porch. If you aren't in there's a few options: a) they deliver it to a neighbour and post a card through your door saying "it's been left at number X"; b) they leave it in a safe space (typically throw it over your garden fence); or c) return it to the delivery office for you to specify when to redeliver or pick it up yourself.
Can anyone shed any light as to why (a) doesn't seem to be used in the US?
Can anyone shed any light as to why (a) doesn't seem to be used in the US?