use Environment variables.
create a php file to define the email Environment variable:
$_ENV['email'] = "firstname.lastname@example.org";
on the page you will add Universal Email, use a require_once() to include the file that defines the variable:
<?php require_once("vars.php"); ?>
open the bindings panel, and click the plus button, select Environment Variable, name the binding the same as the variable you created, "email".
then in universal email, you can select the Environment variable from the bindings panel.