From various sources (http://share.ez.no/forums/suggestions/improvements_to_registration_process/(from)/ez.no/, http://share.ez.no/forums/developer/user-confirmation-for-the-notification-feature) it looks like a

[UserSettings]
EmailRegistrationInfo=enabled

setting existed in the past in order to control whether the confirmation mail sent to the user, just after he validated his account, was sent or not.

Did this ever existed?

Anyway, having that feature would be nice since there is no way to hook in that process.

Original share.ez.no thread: http://share.ez.no/forums/install-configuration/what-is-the-best-way-to-disable-the-user-registration-e-mail-sent-to-the-user