imperialWicket's approach would still work fine in that case when john@dk clicks the "Yes, that's really my email adress" button - and I suspect he'd be pleasantly surprised to see it work, I'll bet he's got a very high expectation of that address failing completely on most websites...

I have a cow-orker who's first name is "G" - he's very used to poorly-validating websites claiming that his firstname is "wrong".