Limit the contacts that appear to a user when sharing to contact only within their "Groups"?

[eldelacajita]

I enabled this option under ‘Sharing’ settings: “Restrict users to only share with users in their groups”

It seems to work just fine. Users that don’t have a group in common won’t see their names autocompleted/suggested while trying to share something, but they can still share things between them if they know their full federated cloud ID like user@server.com. So users without a group in common are invisible to each other by default.

That does the trick for us.