Unsubscribe from emails without logging in

There is currently no way to unsubscribe from a phpBB board's emails without first logging in. Whenever an old topic on a board gets bumped and/or becomes active again, there will likely be a number of users who no longer care about the site (and don't remember their credentials) and yet receive notification emails. To unsubscribe, they have to login, which means resetting their password.