Hate to break it to you, but this sounds like a logistical nightmare. First off, tons of postal services don't allow you to mail money (and if you did, it would not be insured). There's the issue of the mailman stealing the money, or someone on your receiving end stealing the money, or lost packages, etc etc.

Also, people would have to trust you. And the postal system. And your workers. And their luck...

USDT is just a lot easier, and it's more legal and established too.