cooperative-market/beescoop_pos/static/src/xml/templates.xml

<?xml version="1.0" encoding="UTF-8"?>
<templates id="template">
    <t t-extend="ReceiptScreenWidget">
        <t t-jquery='.pos-receipt-container' t-operation='before'>
            <div class="button send">
                <i class='fa fa-envelope'></i> Send Receipt By Mail
            </div>
        </t>
    </t>
</templates>