It works if using Compiler's version of the software. However if you download the file separately, under
addon_pmail_options.php there are no added code fragment to the
$loginLogout setting. It should look that way:
$loginLogout='<input type="button" name="submbut" value="'.$l_pmSend.'" class="inputButton" tabindex="5" onclick="JavaScript:submitForm();" /> <input type="button" value="Preview" class="inputButton" onclick="previewMessage();" />';
I.e. you shall add this string to
$loginLogout to let it work with PM.