would be nice if what valid means was clearly defined before the test. what the rfc's regex allows is probably the least useful way to think about email validation.
I see some of the sibling comments seem to imply that "valid" means that it's deliverable at that moment in time, which would make producing a quiz like this some nonsense because then they'd have to actually register xn--tp8h as a domain, and create an MX record for it
