That's more of a proof that regexes can't do everything, than a proof email is bad.
Edit: The following is completely wrong
For example, the python module to parse an email address is around 500 lines and repeatedly warns it'll be very hard to follow without a copy of the spec in front of you. It contains code for parsing multiple timezone formats and cite to a follow up spec addressing a bug in the initial treatment of negative timezones...
https://github.com/python/cpython/blob/master/Lib/email/_par...
The code I wrote for parsing email headers is here: https://github.com/jcranmer/jsmime/blob/emailutils/headerpar... . A decent chunk of it is building a full lexer for email headers, and trying to cope with only supporting internationalization support in a few cases where they need to be supported. And the corner cases for that i18n support are really nasty.