The pragmatic answer is that, the USPS tried it 2-3 times in its history, but was continually hobbled by private industry lobbyists, until in 2006 when it was f

The pragmatic answer is that, the USPS tried it 2-3 times in its history, but was continually hobbled by private industry lobbyists, until in 2006 when it was finally banned from ever trying anything again: https://www.bloomberg.com/features/2016-usps-email/ https://www.bloomberg.com/features/2016-usps-email/