YSK the USPS has a free online service called Informed Delivery that lets you see photo scans of upcoming (same-day) and recent mail to your home.

You can sign up for free at http://ift.tt/2nTZzHX and there's a more detailed FAQ at http://ift.tt/2rQ4vjj. It's great if you're out of town and want to keep up with your mail (even if it's being held), and of course it lets you know if something didn't make it from the post office to you. Scans aren't available for packages but there is a dashboard for incoming packages including tracking number and ETA.