[gemma]

This is marginally tangential (because the Intelligent Mail tracking programs are completely separate from the tracking the article references), but tracking mail is hugely important to the USPS. Giant postal customers who individually mail millions of pieces every month want end-to-end routing metrics, and the USPS itself uses tracking for their own internal reporting. It's how they know quickly when a service facility is overloaded, and it's how AT&T knows your bill last month made it to your front door (or at least to your local Post Office).

Assuming you're in the US, check some of the mail you've received recently; do you see a jagged-looking barcode on the front? It can uniquely identify that specific piece, as well as the mailer and any special services applied--mostly requesting higher levels of tracking. The metadata for that piece lives in a big postal database in the sky, where mailers can request access at varying levels of detail. The USPS is way past just delivering mail at this point.

(Source: I was a developer in the postal mail industry for six years.)