I particularly like the unsubscribe pages that have broken email validation. Sign up for a service with me+service@gmail.com just fine, but the unsubscribe page

I particularly like the unsubscribe pages that have broken email validation. Sign up for a service with me+service@gmail.com just fine, but the unsubscribe page won't accept the '+'. Or the ones that require you to sign in update your spam preferences. Ugh.