My neighborhood has an even simpler system. We all have individual mailboxes, and then there are a few larger mailboxes for packages. When the mailman delivers a large package, he puts it in one of the package boxes, locks it, then puts the key in the mailbox belonging to the recipient. The recipient then gets the key with the rest of their mail, which they use to get to the package. The package locks are designed to capture the key once you use them, so only the mailman can retrieve the key and use it again next time.