- filter_var: documentation ( source)
<?php
$email = 'johnsnow@ヒキワリ.ナットウ.com';
$email = idn_to_ascii($email);
//$email = str_replace('xn--', '', $email);
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
echo 'valid';
} else {
echo 'not valid';
}