This wasn't always the case. People had to advocate for it, and FCC policy (Wireless Local Number Portability) had to change. It didn't happen until 2003 in the US. It won't be any different for emails and domains: someone has to push for that change.
Email is intrinsically an unreliable service, and always has been. It's a "best-effort" service. But at least email is honest about it up-front, and tries to address reliability in the RFCs.
Not that Google cares much about RFCs.
In case of email, it probably should simpler. Gov only serves as an address book, essentially. But does minimum of tech implementing it. Given how domain MX records work, does not seem possible. So i think email relay is the closest thing.
As far as USPS anti-tampering and enforcement goes: <hollow laugh>. The postmen robbed me silly, and there was no process to get it fixed.