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Comment by mnarayan01 | Hacker News Reader

> or a valid email regexp

In terms of standards, there's not a whole lot you can do beyond validate the domain if it includes one. You can take the HTML5 approach (https://developer.mozilla.org/en-US/docs/Web/HTML/Element/in...), but that means leaving out at least theoretically valid email addresses.

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Huh? RFC 2822 describes in detail what a valid email address looks like. (There might be newer ones superseding it; that's the one that was current back when I looked into this topic.)

In practice, a lot of theoretically valid email addresses are rejected by implementations, e.g. my favorite:

  "@"@example.com

What's true, of course, is that you should never rely on an email address being syntactically correct. You should only use it after having done a validation process that involves sending mail to that address.

I agree with everything you're saying (though my favorite is probably addresses containing newlines). My point is just that in practice it's not terribly useful, e.g. why HTML5 defines its own: https://html.spec.whatwg.org/multipage/input.html#valid-e-ma....

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