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 /**
 * WooCommerce Extra Feature
 * --------------------------
 *
 * Add another email recipient when an order is completed
 *
 */
function woo_extra_email_recipient($recipient, $object) {
    $recipient = $recipient . ', your@email.com';
    return $recipient;
}
add_filter( 'woocommerce_email_recipient_customer_completed_order', 'woo_extra_email_recipient', 10, 2);