While you and Ovid
are both correct, context is important. Just because all of those email addresses are valid WRT the RFC, they likely are not valid for a given MTA. It is also
probable that an MTA accepts email addresses as valid that are categorized as invalid by the RFC. Having spent a couple of years managing an enterprise email gateway, I have seen what happens when two MTAs can't agree on what is and is not valid.
My whole point being is that - right or wrong, a simple form of a regex can work for validating email addresses when what governs valid is local environment and not the global RFC.