Hi,

To do it from UI: (This will be deleted if you upgraded the stock module)

Enable developer mode and Go to settings -> Technical -> Email Templates, Search for "Delivery: Send by Email" and then open it, click on Edit and in Email Configuration tab, in To (Emails) paste the below:

{{object.sale_id.user_id.email_formatted}}

To do it using custom module, you need to 

<?xml version = "1.0"?>

<odoo>

    <data noupdate="1">

        <!-- Make the record updatable -->

        <function name="write" model="ir.model.data">

            <function name="search" model="ir.model.data">

                <value eval=" [('name', '=', 'mail_template_data_delivery_confirmation'), ('module', '=', 'stock')] "/>

            </function>

            <value eval="{'noupdate': False}"/>

        </function>

   

        <!-- Inherit Email template -->

        <record id="stock.mail_template_data_delivery_confirmation" model="mail.template">

            <field name="email_to">${object.sale_id.user_id.email_formatted|safe}</field>

        </record>



        <!-- Set the record inupdatable -->

        <function name="write" model="ir.model.data">

            <function name="search" model="ir.model.data">

                <value eval="[('name', '=', 'mail_template_data_delivery_confirmation'), ('module', '=', 'stock')] "/>

            </function>

            <value eval="{'noupdate': True} "/>

        </function>

    </data>

</odoo>