Although… snail mail is also legislated to be secure. It’s not used as often because there is a more convenient, better(?) alternative: fax. I wish some funding for so-called “AI” projects could be used to develop even more convenient/better alternatives to fax. There are messaging protocols but they seemed crazy.
Payment systems are crazy too. Stripe did all the boring work and now there is a convenient interface for payment processing: Stripe’s HTTP API.