This still sounds like it might be a clunky solution to whatever the root problem is. What I would have like to have seen in the original question is more specificity about the requirements. Because most of the information was actually in the title of the question, we were left to assume the details of the requirements for ourselves.

If someone is ordering something via your client's website, you do not need to use any page scrapers or anything else. Simply add a field for e-mail address and an opt-out checkbox to a form during the order process. Salvadors' link below looks to be a good way to validate the email addresses. Store the valid addresses in your customer records along with the other customer data.