Opting in to mailings

Can a feature be introduced to show on 3rd party website enquiries whether the applicant has opted in or out of future mailings. If they have opted out they are effectively one use only for that enquiry and we can’t send them details of other potentially suitable properties in the future. An ability to opt them back in, with their consent, would be a very useful feature, but more so to know in the first place if they have opted out, becasue if they have, the enquiry is of no further use !