Item arrived yesterday, but buyer asked me if it was sent already!!!

Someone correct me if I'm wrong. As far as the postal customer is concerned, "delivered" indicates the packaged has arrived at the intended destination, not just the city. Perhaps the logistics are so that the package arrives and is handed to the postal carrier for delivery, and it's at that point, and not after it was delivered, the USPS reports the package as "delivered." The postal carrier could burst into flames and not deliver the package. Then that's the USPS' problem, not the sender's. Delivered means delivered to the person who purchases that service. Doesn't it?
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No, not delivered until the mailman scans the package at your door to say delivered or scans the package at your door to say delivery attempted.