using a template for the email, in order to refer to column from the recordset that drives the to address, add the following code at line 1 of the email template file:
<?php
global $RecipArray;
global $RecipIndex;
?>
you will need to create another recordset that looks up data from the relating table using the id from the users table to filter the relating column, for example, if the ID column of the main table is "ID" set the filtering of the recordset to Server Variable and enter the following:
$RecipArray[$RecipIndex][0]["ID"]
then use the bindings panel to add the recordset data to the message, and add repeat region.