[philderbeast]

"A "this doesn't look like an email-address"

unfortunately this also needs to be done server side, unless your trusting the client to send you information that is what your expecting?

client side validation makes for a good user experience, but it does not replace the requirement to validate things server side, and many times you will end up doing the same validations for different reasons.

[berkes]

"It depends".

If it's merely a hint for the user (did you make a typo?) there's no need to ensure "this is a valid email address". in fact: [e-mail] is perfect valid email-address, but quite likely (though not certain!) not what the user meant.

I've seen hundreds of email-adres-format-validations in my career, server-side. The most horrible regexps, the most naïve assumptions[1]. But to what end?

What -this is a question that a domain expert or business should answer - does it matter if an email is valid? [e-mail] is probably valid. As is [e-mail][2]. What your business- expert quite likely will answer is something in line of "we need to be sure we can send stuff so that the recipient will can/read it", which is a good business constraint, but one that cannot be solved by validating the format of an email. One possible correct "validation" is to send some token to the email, and when that token is then entered, you -the business- can be sure that at least at this point in time, the user can read mail at that address.

[1] A recent gig was a Saas where a naïve implementor, years ago, decided that email-addresses always had a TLD of two or three letters: .com or .us and such. Many of their customers now have .shop or somesuch. [2] Many devs don't realize that `foo` is a valid email-adress. That's foo without any @ or whatever. It's a local one, so rather niche and hardly used in practice; but if you decide "I'll just validate using the RFC, you'll be letting through such addresses too!". Another reason not to validate the format of email: it's arbitrary and you'll end up with lots of emails that are formatted correct, but cannot be used anyway.

[bigtunacan]

Just because some places implemented the validation wrong does not mean the validation should not occur.

The validation is there to catch user mistakes before sending a validation email and ending up with unusable account creation.

[berkes]

You are missing the point. Sorry for that.

It doesn't matter if an email has a valid format: that says almost nothing about it's validity. The only way you can be sure an address can receive mail(today) is by sending mail to it. All the rest is theatre.

And all this only matters if the business cares about deliverability in the first place.

[bigtunacan]

No, I understood your point and I agree sending the email and getting some type of read receipt is necessary.

You seem to think that because of this client validation should be skipped. On that point I disagree. If you can tell that it's not a valid email address (bigtunacan@goog obviously invalid since missing a TLD) then no email should be sent. Good UX is to let the customer/user know there is a mistake in the email address.