In case anyone is having trouble with the above code, here is an unsubscribe static page that works for 4.0.18:
Code:
<form action="mail/unsubscribe.php" method="post" name="unsubscribeform">
<table><tr><td><input type="text" name="email" size="40"></td><td>{include file="buttons/button.tpl" type="input" style="button" button_title="unsubscribe" href="javascript:document.unsubscribeform.submit()"}</td></tr></table>
<input type=hidden name=redirect value="{$redirect}">
</form>