When I decided to learn more about regular expressions back in 2002-2003 I found a regular expression for RFC822 (with comments removed): http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html

As an exercise, I deconstructed that into the pieces it was built from. Funny times :)

Don't see a timestamp on your link, but i suspect this one is more correct:

https://metacpan.org/source/RJBS/Email-Valid-1.202/lib/Email...

I prefer /@/

https://davidcel.is/posts/stop-validating-email-addresses-wi...

This is the only sane way.

Until for some reason a user really needs to use a classic UUCP bang-path. Poor help!trapped!in!lost!server ;)