The HTML email regex validation [1] is probably the best rule to use for validating an email address in most user applications. It prohibits IP address domain literals (which the emailcore people have basically said is of limited utility [2]), and quoted strings in the localpart. Its biggest fault is allowing multiple dots to appear next to each other, which is a lot of faff to put in a regex when you already have to individually spell out every special character in atext.

[1] https://html.spec.whatwg.org/multipage/input.html#email-stat...

[2] https://datatracker.ietf.org/doc/draft-ietf-emailcore-as/