How to make majordomo request confirmations of subscriptions?

Hi All, I would like to set up my majordomo to request subscription confirmations from users, by sending them a cookie. Looking at the majordomo config files, I have not found such option. Ideally I would like to have a system that a) requires the new users confirm new subscriptions and b) once in a while as users to confirm their existing subscriptions. Is there any way to do it? Thank you. - Igor.