Oh, right, the redirect is killing the POST collection.
set the redirect to:
contact.php?sent=true&email=<?php echo((isset($_POST["fieldset_group_Name"]))?$_POST["fieldset_group_Name"]:"") ?>
This way the posted email address is captured into the get collection.
then set the display to:
<?php if(isset($_GET['sent']) && $_GET['sent'] == "true") { ?>
<div class="confirm">Thank You<?php echo((isset($_GET["email"]))?$_GET["email"]:"") ?><br />
We will reply shortly. </div>
<?php } ?>