palette/views/jst/messages/sendForm.handlebars

<form action="{{location}}" method="post" class="bootstrap-form message-send-form">
  <div class="fields">
    <label for="message-send-body">{{#t "labels.message_body"}}Message{{/t}}</label>
    <textarea name="message" class="input-xlarge" id="message-send-body"></textarea>

    <input type="hidden" name="from" value="{{from}}" />
    <input type="hidden" name="subject" value="{{subject}}" />
    <input type="hidden" name="secure_id" value="{{secureId}}" />
    <input type="hidden" name="message_id" value="{{messageId}}" />
  </div>

  <div class="actions">
    <button type="submit" class="btn btn-primary">{{#t "labels.send_button"}}Send{{/t}}</button>
  </div>
</form>