sanity check to confirm it's an email-able domain

Reading Malcolm McDonald's  Web Security for Developers: Real Threats, Practical Defense for a class I am instructing, he mentioned this Python tidbit that can check if a given domain is likely setup to handle email:
import dns.resolver
def email_domain_is_valid(domain):
  for _ in dns.resolver.query(domain, 'MX'):
    return True
  return False
 

I asked ChatGPT for the PHP equivalent:

function emailDomainIsValid($domain) {
    return checkdnsrr($domain, "MX");
}


and then a version where I can just pass in the full address, and it will get a clean version of the email address, or else return false:

function cleanEmailWithValidDomain($email) {
    // Trim whitespace from the email
    $email = trim($email);

    // Validate the email address
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        return false;
    }

    // Extract the domain from the email address
    $domain = substr(strrchr($email, "@"), 1);

    // Check for MX records
    if (checkdnsrr($domain, "MX")) {
        return $email;
    }

    return false;
}

Somehow I missed that you could do that kind of serverside check; I think I read "you can't really tell if an email is legit" too much to heart.