Fwiw, junk mail isn't taxpayer subsidized, they pay a different rate. It's actually a profit center for USPS.

I have to subsidize them by maintaining the box so they can save labor and don't have to walk up to my door to deliver spam.

The spam is a profit center for the USPS, it's what allows them to deliver other mail cheaper than UPS/FedEx.

This must vary by location. My box was purchased initially by the neighborhood but is maintained by the USPS. My mom's house gets walk-up service with mail through a slot. Aside from buying stamps or paying to send a package, I have never directly subsidized USPS infrastructure. Excluding the punitive pension requirements Congress uses to make USPS look like a money pit, they'd probably be profitable.

In more rural areas there are not neighborhood boxes like that. Each person is responsible for an individual box by the road.

It amazes me that the environmental activists haven’t taken this up as an issue yet. The amount of spam I receive is enormous and there’s no way out.