the email feild in your form is "Submit_group_Email":
<input id="Submit_group_Email" name="Submit_group_Email" type="text" value="" class="formTextfield_Large" tabindex="2" onblur="hideServerError('Submit_group_Email_ServerError');"/>
you should change the from and cc to:
<?php echo ((isset($_POST["Submit_group_Email"]))?$_POST["Submit_group_Email"]:""); ?>