This basically happened to me on a site, sans cookie. It sent notifications when customers left reviews. The convenient user experience is, when someone leaves

This basically happened to me on a site, sans cookie. It sent notifications when customers left reviews. The convenient user experience is, when someone leaves a review, to forward the email with the review to the customer and ask how we can help. After doing this a few times I realised it had small links in the footer to login and administrate without a password, using tokenised links. Support had no way to expire these. I needed to create and migrate a new account (which incidentally ended up emailing hundreds of people for reviews they left months and years ago).