...the United States Postal Service has tracking numbers and tracking website. I've never seen a more poorly articulated idea in internet land.
I frequently order items from Amazon.com. Occasionally packages are sent via USPS but often me my packages come via UPS. Now there's a tracking system. I can follow my packages from Memphis to Illinois to California to Istanbul. I have a pretty good idea what day my packages are going to be delivered, also.
The post office on the other hand doesn't have a clue where my package is and when it will be delivered. It is usually delivered before the tracking software shows it being picked up.