Set a default sharing restriction for Google+ content

You can control whether your users' posts can be shared outside your organization’s G Suite domain by default. If a post is restricted, people in your domain who receive it can't share it with anyone outside your domain.

If you restrict sharing posts, other Google+ content is also affected. New communities are restricted to your organization’s domain by default, and users' +1 notifications are always restricted

To restrict user content to your organization’s domain by default:​

1. Sign in to your Google Admin console.

   Sign in using your administrator account (does not end in @gmail.com).

2. From the Admin console Home page, go to AppsG SuiteGoogle+.

3. Click Advanced Settings.

4. In the Sharing posts section, select Make the default setting for new posts restricted. 
   Although you can set a default sharing restriction, users can still override this restriction for individual posts or for the communities they create.