app-MAIL-temp/templates/admin/model/newsletter-list.html

{#
Add custom input form so admin can enter a user id to send a newsletter to
Based on https://github.com/flask-admin/flask-admin/issues/974#issuecomment-168215285
#}
{% extends 'admin/model/list.html' %}

{% block model_menu_bar_before_filters %}

  <br>
  <li id="here" class="form-row">
    <input name="user_id"
           class="form-control"
           placeholder="User ID"
           aria-describedby="userID" />
    <input name="to_address"
           class="form-control"
           placeholder="Specify an address to receive the newsletter for testing"
           aria-describedby="Email address" />
  </li>
{% endblock %}
{% block tail %}

  {{ super() }}
  <script type="application/javascript">
        $("input[name='user_id']").appendTo($("#action_form"))
        $("input[name='to_address']").appendTo($("#action_form"))
        $("#action_form").appendTo($("#here"))
        $("#action_form").attr("style", "")
  </script>
{% endblock %}