I would bet in most organizations you can find a copy-pasted version of the top SO answer for email regex in their language of choice, and if you chase down the original commit author they couldn't explain how it works.
I think it's impossible to actually write an email regex because addresses can have arbitrarily deeply nested escaping. I may have that wrong. I'd hope that regex would be .+@.+ and that's it (watch me get Cunninghammed because there is some valid address wherein those plusses should be stars).
