My favorite regex is the E-Mail Regex[1].
Works 99.99% of the time, is unreadable/unmaintainable, makes you understand that the only true way to verify an e-mail is to send an e-mail to that address.
[1] - https://emailregex.com/
PS: Gotta love the Perl / Ruby version
The only way you should ever "validate" an email address with a regex is like this: /@/
I suppose it depends on what we mean by validate. Running an ecommerce site, I got a lot of mileage out of prompting the customer to fix emails that "looked wrong". We allowed them to proceed if they wanted. A really common one was "[email protected]" when "[email protected]" was wanted. We used a slightly modified version of https://github.com/mailcheck/mailcheck and found it to be really useful.