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".
I've got another friend/acquaintance who's got a fully legal (self chosen) single name. No first/middle/last name, just a "mononym". He has the expected hilarious outcomes with things like Google's "real name policy".
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".