Universal Email will create the script that will send the email for you but it will be up to you to create the other parts of this. I think you should start out with a page that has a recordset on it that selects all the customers who expire in five days. You would then use Universal Email to setup the message and send it to everyone in the recordset.
To automate this you will need to setup a chron job or scheduled task depending on your server environment. Both of these would work the same way, you preconfigure the settings of what script you want to run (the page) and when. You should do this daily so that you everyone gets an early warning about the expiration.