Most of the online vouchers now require you to sign up with your details in order to recieve the discount. Effectively, they are offering a £1 voucher in return for unending supplies of spam. I don't mind this for loyalty schemes because you get long term bonuses and savings, but to accept spam forever in return for a one-off voucher seems like they aren't offering very much. Do you go for these deals, use a disposable email address, or just not bother with them?
Yes, online marketing has become quite popular these days. These sites trick you into signing up and then spam your email with useless posts and info. It is better off not accepting the deals they promise by compromising on your email id. Instead, if you still wish to receive their deal because it is a better one, try signing up with your email. The moment you receive the first promotional email from them, filter that email as "spam" and add the sender's email id to the spam list. Any further emails from them would directly go into your spam folder without bothering you.