Set a default sharing restriction for posts
If you've activated Google+ premium features for your organization, you can control whether your users' posts can be shared outside your organization by default. If a post disallows external sharing, anyone in your organization who received it can't share it with people outside your organization.
Note that although you can set a default sharing restriction, users can override this restriction for individual posts.
Currently, if you choose to restrict posts by default, your users can't access their Google+ account from the Google+ mobile app.
To set a default sharing restriction:
Sign in to your administrator control panel.
The URL is https://www.google.com/a/cpanel/primary-domain-name
, where primary-domain-name is the domain name you used to sign up for Google Apps.
Go to Settings > Google+ > Org Settings.
Under Sharing posts, choose one of the following:
Unrestricted, meaning users can share posts with anyone.
Restricted, meaning users can share posts only with members of your organization.
Click Save changes.
Note: If you later deactivate Google+ premium features, sharing restrictions on existing posts will remain. However, the default sharing restriction will not be applied to new posts.