Programmers don't get things right with that precision either. They get it right only after many cycles of feedback and iteration. From many layers: the IDE, the compiler, code analysis tools, and finally runtime behavior.

Postal mail addressing doesn't permit any sort of feedback loop. The "user" has no indication at mailing time of any problems with the address. So it's no surprise that errors are common.

If you want email addresses to be correct, then you need that feedback loop, which means email verification.