Great insight. However, the error message does not prompt another action or pause your typing. Also, just that you brought the @ button, its always on the number key 2, on keyboards; in case of tabs or mobile when a user enters on email field, best practice would be to alread have @ and .com on separate keys(most of them already do it) for ease of input.

Speaking of what I mean by validating the field immediately, I suggest to do so before hitting on submit button and then getting list with load of errors in my form.

Thank you for raising this insight, it encourages more thought in simple forms.