We use a plugin from DPD, when selecting 10 orders, clicking on 'create labels' wil make the shipping labels. But the plugin doesn't send a mail to the user. So we have to open each order, go to shipping details, click on that shipment, and then we can click on the button: "send tracking information".
This button has this url: https://ourwebsite/index.php/admin/sales_order_shipment/email/shipment_id/120900/key/e421b330f76db120ef8be158c0d7ae07/
I adjusted the function and rebuild the exact dynamical url.