- substr: documentation ( source)
- substr_count: documentation ( source)
- var_dump: documentation ( source)
- strpos: documentation ( source)
- checkdnsrr: documentation ( source)
<?php
$email = 'test@io';
var_dump((substr_count($email, '@') === 1) && (checkdnsrr(substr($email, strpos($email, '@'))) || checkdnsrr(substr($email, strpos($email, '@')), 'A')));