<iframe name="myframe" style="display:none" onload="Donetest(this)"></iframe>
<form id="post" method="post" action="/send.php" target="myframe">
<p><input name="action" value=""/> action</p>
<p><input name="name" value=""/> name</p>
<p><input name="tel" value=""/> tel</p>
<p><input name="city" value=""/> city</p>
<p><input name="email" value=""/> email</p>
<p><input type="file" name="fileAttach"> fileAttach</p>
<input type="submit">
</form>
<script type="text/javascript">
function Donetest(frame) {
alert($(frame).contents().find("body").html()); //тут проверяем, - что вернулось
}
</script>