Maybe some middle road: + Netflix can send an email about optionally(!) confirming a user's address. + Now, rather than disabling all features and slowing dow

Maybe some middle road: + Netflix can send an email about optionally(!) confirming a user's address. + Now, rather than disabling all features and slowing down on-boarding it is possible to update the communication towards unregistered users. + If an email has to be sent to an unconfirmed address, preceed it with a warning. If pietjepuk@gmail.com has been confirmed, but pietje.puk@gmail.com not, emails for the latter will have this warning automatically. + Remaining option: do you want to send regular safety requests to unconfirmed addresses as provider? Policy might differ. However, it is possible to use this email to tell the user about safety/security w.r.t. your system. I'd say yes.