$addressList = array();

foreach ($arrOrderDetail as $orderDetail) {
    $productId = $orderDetail["product_id"];
    
    // 商品データごとのメールアドレス取得
    $arrProduct = $objQuery->select("comment4", "dtb_products", "product_id = ?", array($productId));
    $addressList[] = $arrProduct[0]["comment4"];
}

// $addressList[]をBccに利用
$bcc = $arrInfo['email01'] . "," . implode(",", $addressList);