Mail signup

My client runs newspaper ads on a weekly to bi-weekly basis for new customers to visit website to obtain coupons, special offers, etc. We would like to have a script that would check for the e-mail address of the person signing up. If they HAVE NOT signed up, they can continue on to signup form and receive the offer. If they HAVE already signed up for that offer once, they would be redirected to a page saying something like "sorry, that offer has already been sent to this e-mail address". I currently use CGI/Perl scripting with an auto-responder to send out coupons to people who signup on the site. I have also programmed the script to print on the coupon/certificate the name and e-mail address of the person who signed up to try to prevent fraud. I am using Visual Form Mail Professional to create most of my scripts. I use DreamWeaver MX 2004 to create the sites, forms, etc. This site is hosted on a Cold Fusion Server. We are utilizing CGI from a 3rd party host since they do not support CGI. The script could be done in Cold Fusion if need be. The company's site was originally all Cold Fusion but now they are only utilizing it with ordering, daily sales forms, e-mail, viewing reports and document management.