Near the bottom of /includes/classes/order.php, you have this:
Code:
zen_mail('', SEND_EXTRA_ORDER_EMAILS_TO, SEND_EXTRA_NEW_ORDERS_EMAILS_TO_SUBJECT . ' ' . EMAIL_TEXT_SUBJECT . EMAIL_ORDER_NUMBER_SUBJECT . $zf_insert_id,
$email_order . $extra_info['TEXT'], STORE_NAME, EMAIL_FROM, $html_msg, 'checkout_extra');
change like this:
Code:
zen_mail('', SEND_EXTRA_ORDER_EMAILS_TO, SEND_EXTRA_NEW_ORDERS_EMAILS_TO_SUBJECT . ' ' . EMAIL_TEXT_SUBJECT . EMAIL_ORDER_NUMBER_SUBJECT . $zf_insert_id . ($_SESSION['payment']=='cod' ? '(COD) ' : ''),
$email_order . $extra_info['TEXT'], STORE_NAME, EMAIL_FROM, $html_msg, 'checkout_extra');