social/mass_mailing_custom_unsubscribe/templates/general_reason_form.xml

<?xml version="1.0" encoding="utf-8" ?>
<!-- Copyright 2016 Jairo Llopis <jairo.llopis@tecnativa.com>
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>

    <template id="reason" name="UI for Providing Unsubscription Reasons">
        <div t-attf-class="js_unsubscription_reason #{extra_class or ''}">
            <div class="col-md-12 mt16">
                Before unsubscribing, could you please tell us why do you want to unsubscribe?
            </div>
            <div class="col-md-12 mb16">
                <input
                    type="hidden"
                    name="res_id"
                    t-att-value="res_id"/>
                <input
                    type="hidden"
                    name="email"
                    t-att-value="email"/>
                <input
                    type="hidden"
                    name="token"
                    t-att-value="token"/>
                <t t-foreach="reasons" t-as="reason">
                    <div class="radio">
                        <label>
                            <input
                                type="radio"
                                name="reason_id"
                                t-att-data-details-required="reason.details_required"
                                t-att-value="reason.id"/>
                            <t t-esc="reason.display_name"/>
                        </label>
                    </div>
                </t>
                <div t-attf-class="form-group">
                    <textarea
                        name="details"
                        class="form-control"
                        placeholder="I am unsubscribing because..."
                        rows="3"/>
                </div>
            </div>
        </div>
    </template>

    <template id="reason_form"
              name="Unsubscription Reason Form">
        <t t-call="website.layout">
            <div id="wrap" class="oe_structure oe_empty">
                <section class="mt16 mb16">
                    <form
                        id="reason_form"
                        class="container"
                        t-attf-action="/mail/mailing/#{mailing.id}/unsubscribe"
                        method="post">
                        <input
                            type="hidden"
                            name="csrf_token"
                            t-att-value="request.csrf_token()"/>
                        <div class="row">
                            <div class="col-md-12 text-center mt16 mb32">
                                <h2>
                                    Mailing Unsubscription
                                </h2>
                            </div>
                            <t t-call="mass_mailing_custom_unsubscribe.reason"/>
                            <div class="form-group mb16 mt16">
                                <button type="submit" class="btn btn-danger">
                                    Unsubscribe now
                                </button>
                                <p class="help-block">Thank you!</p>
                            </div>
                        </div>
                    </form>
                </section>
            </div>
        </t>
    </template>

</odoo>