mautic-checkout-capture-email.html

<div style="display: none;">
  <script type="text/javascript" src="//your.mautic.domain/form/generate.js?id=1"></script>
</div>

<script>
  jQuery("input#billing_email").change(function() {
    var customer_email = jQuery("input#billing_email").val();
    jQuery("input#mauticform_input_yourformname_email").val(customer_email)
    jQuery("form#mauticform_yourformname").submit();
  })
</script>