How to Add an organization-wide group:

1. When you create a new group, check Add all users within your-domain to this group in the Create new group dialog box.
2. Your new group is created and the name appears on the Groups page.
3. Click the name of your group to open the settings page and click Manage users.
4. The group's member list now includes a special new member called All users within your-domain.

You can't edit the members within the All users within your-domain member. But just like any other group, you can edit the groups access settings or delete it.