For future reference, this is what you have to do now:
Change "Configuring privileges for..." from "Global" to each category. You can then remove all "Guest" privileges.
I was thinking is there a way to restrict a category only to users with certain email provider like yahoo or Gmail ?
Is it possible?
You could probably use the registration email plugin and rather than deny entry, place them into a group.
A proper plugin dev may have a better idea of what to use.