Using Better Blogs
Space Administrators can access 'Blog watchers' via Space Tools -> Add-ons:
View current blog watchers of a space
Space Administrators can view the users and groups currently subscribed to a space blog.
Add user or group as blog watcher
Space Administrators can add a user or group to blog watchers.
Opt-out of group notifications
Users subscribed to blog notifications as part of a group can opt-out of notifications by clicking Unsubscribe at the bottom of any email notification.
Existing behaviour is retained for those users who have subscribed themselves to blog notifications.
It is also possible for Space Administrators to disable the Unsubscribe functionality. This is on a per-space basis: