СП
add_action('phpmailer_init', function (PHPMailer $phpmailer) {
$phpmailer->DKIM_domain = 'XXX';
$phpmailer->DKIM_private = 'XXX';
$phpmailer->DKIM_selector = 'mail';
$phpmailer->DKIM_passphrase = '';
$phpmailer->DKIM_identity = $phpmailer->From;
});

