Thanks Jason. Great, it worked.
Embarrassing to admit missing that.
Finally, I created the following response using UE email body editor page, however the link in center should open my confirmation page but is instead causing a server 500 error on submit. Does the code look valid or is there another UE related issue?
<p>Dear <?php echo ((isset($_POST["mem_fname"]))?$_POST["mem_fname"]:"")?>,</p>
<p>Thank you for joining us.</p>
<p>In order to confirm and activate your membership, please either click on the link below
or copy and paste it into your internet browser. </p>
<a href="http://homes.crazyplum.com/members/confirm.php?UID=<?php echo (mysql_insert_id())?>&ID=<? echo ((isset($_POST["mem_conf_id"]))?$_POST["mem_conf_id"]:"")">Click here to complete the account setup.</a>
<p>Your password is <?php echo ((isset($_POST["mem_password"]))?$_POST["mem_password"]:"")?></p>
<p>Thankyou and regards, </p>
<p>Crayplum Homes Website Team </p>