How to auto-fill customer email in Shopify shipping notification code?

To automatically have ordernumber and email address filled in once the customer clicks to a customized tracking link I need to know the {{ code }} ?? to fetch email address of the customer where the Shopify notification is being send too. I already know that the ordernumber has this code: {{ order_name }}

Can anyone help me with this? So to clarify, need to automatically fill in the customer email address

Thanks in advance!