mailtrain/views/subscription/partials/subscription-unsubscribe-form.hbs

<form method="post" id="main-form" action="/subscription/{{lcid}}/unsubscribe">
    <input type="hidden" name="_csrf" value="{{csrfToken}}">
    <input type="hidden" name="campaign" value="{{campaign}}">
    <input type="hidden" name="ucid" value="{{ucid}}">

    <div class="form-group">
        <label for="email">{{#translate}}Email address{{/translate}}</label>
        <input type="email" name="email" id="email" placeholder="" value="{{email}}" readonly>
    </div>

    <button type="submit" style="position: absolute; top: -9999px; left: -9999px;">{{#translate}}Unsubscribe{{/translate}}</button>
</form>