> From what I can tell this was a capability the USPS has had for a while, probably going back to the days of anthrax spores being sent to politicians. The USPS was probably directed to track where every piece of mail came from and image the outside of it.

I don’t think that’s accurate. They already had the scanning/imaging pipeline for routing and sorting. It wasn’t until later that they realized it’d be a good service to email the images to the recipients every morning – hence, Informed Delivery. It’s like a side-project that grew into a bonafide feature.