Go to one of the emails you have been sent for the retailer you wanted notifications for, there will be a link, for example "Amazon £15 email Gift Voucher", to which you click the link. The link works whether you have logged in or not. Once the link is clicked, you can unsubscribe for this particular retailer (and will be unsubscribed regardless of log in), or click on 'Manage Notifications' where you can unsubscribe from any other notifications you have, though you need to log in for this to work.