What this does is adds an infobox where your visitor can enter their e-mail address to receive newsletters. It also checks to see if the e-mail address already exists in your visitor table, as well as it checks to see if your visitor is really a customer.

If either of those values are true, it will say that account exists already. This prevents multiple newsletters being sent to the same address.

When that visitor turns around and registers for an account, create_account.php will check to see if the e-mail exists in you visitor table. If their e-mail is there, it will delete it and automatically turn their newsletter subscription on.

Also included is HTML support for your newsletter.