don't waste space on compose window. Some people don't have 21 in. monitor

and can't afford all that whitespace and extra rows in compose.

P.S. If you change api and break compose_button_row hook, make sure that core
plugins are updated to new API.

templates/default/compose_buttons.tpl

@@ -52,7 +52,7 @@ extract($t);
   </td>
   <td class="fieldValue">
     <input type="checkbox" name="request_mdn" id="request_mdn" value="1" <?php if ($read_receipt) echo ' checked="checked"'; ?> /><label for="request_mdn"><?php echo _("On Read"); ?></label>
-    <br />
+    &nbsp;
     <input type="checkbox" name="request_dr" id="request_dr" value="1" <?php if ($delivery_receipt) echo ' checked="checked"'; ?> /><label for="request_dr"><?php echo _("On Delivery"); ?></label>
   </td>
  </tr>