[Domenic_S]

> How can a non-RFC-compliant email be valid?

甲斐@黒川.日本 is a non-RFC 5322-compliant, but still valid, email address.

Unless you're implying that "valid" === RFC 5322-compliant, in which case the example isn't valid ;)

The best way to validate an email address: send an email to that email address containing a confirmation link. Simple, easy.

[rjbond3rd]

Ah, understood. I was thinking "valid == well-formed" without knowing whether it really works (i.e., could be deleted), whereas I see you rightfully point out that it more reasonably means "it works." Thank you, makes sense.