Your organization has enabled Google Groups for Business to let employees create and manage their...

Set the setting for Google Groups for Business called Accessing groups from outside this organization to Private.

In Additional Google Services, turn Google Groups OFF at the root organizational unit.

Use the Directory API to change the settings of user-created groups to disable features that allow external users to access, view, or post on groups.

Set the setting for Google Groups for Business called Default for permission to view conversations to All organization users.