I don’t validate emails, I test them.

Hooray! You get a gold star.

OK, maybe I do some light validation first,

I hope your "validation" does nothing more than show a warning that the user is allowed to ignore.

I have seen too many systems built by people who think they know what's valid or not before and after the @ sign*, and they are almost always dead wrong. In the worst cases, such systems accept an unusual-looking address and claim to send the expected verification message, but never actually send it. Of course, these systems won't work for some people, and since none of their online docs or support staff know why, those people will be locked out of using the system and funneled into bottomless pit of misery if they try. Please don't build broken garbage like this.

*Fun fact: Not so terribly long ago, even the @ sign didn't have to be present. Some email addresses were bang paths. I'm not sure if any of these are still in use, but it wouldn't shock me to learn that they are.