[5teev]

It's an interesting intellectual exercise to build THE email validation regex, but it's shortsighted to inflict your experiment on the public.

While I definitely enjoyed how Friedl's book (http://regex.info/book.html) builds over several chapters to an ever more complex solution, maybe a page long, my takeaway was: don't bother. A friendly UI will help users avoid an obvious mistake, but as other posters have pointed out, the only real validation is, does an email get there?