The only way to validate an email is to send a message to the email address. Validating that it fits the rfc is pointless, because a) its very easy to create an email that is both false and meets the rfc, b) email provider might bypass the rfc and the email would still be working.

To validate user input, I use that: /^[^@]+@[^.]+\..+$/. It's doesn't tell me if the email is semantically correct per the rfc because I'm not running an rfc correctness validation service. What I want is to make sure that users didn't input their name in the email field. This tells me if it ressembles an email

It isn’t pointless. It is fast feedback for typos and form validation

The parent's regular expression covers the most egregious typos without making any assumptions about domain names or tlds. If you wanted to help out with common typos you could add additional logic to specifically check for "*@gmial.com" or other permutations of the common domains. If you wanted to get really fancy, you could even run it by an edit distance function against the common domains and warn if they're close to a common one but not quite there.

Most typos, however, are likely to be in the first part, not in the domain. The only real way to validate against those is to try the address and see.

Otherwise, yeah, most people would be better served by a library that detects domain typos like https://github.com/mailcheck/mailcheck than spending time on regexes.