Your New mail box down the street is someone’s old mail box.
I, often times advise people to have the keys changed when they move into a new home. You just never know who has the old keys.
Did you know that you can also get your mailbox key changed? If it’s a cluster box owned by the post office, USPS will have it re-keyed, give you 3 keys and do it pretty fast. Often, the next day. It costs $40, but it’s well worth it.