wp-includes/PHPMailer/PHPMailer.php:4448Check whether the supplied address uses Unicode in the local part.
$addressbool protected function addressHasUnicodeLocalPart($address) { return (bool) preg_match('/[\x80-\xFF].*@/', $address); }Unchanged from 6.9.7 through 7.1.0.
Signature, return type and hooks compared across 3 parsed releases.
src/wp-includes/PHPMailer/PHPMailer.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.