By default, Google Groups do not allow external (non-ncsu) email addresses to be a member of a Google Group.  Group Managers can directly manage this setting for their groups.

Note: If a group with external members is used for calendar invites or sharing of Google files and folders, the external members will also be included with the same permissions.

Enable External Members

1. Visit groups.google.com.
2. Select My Groups.
3. Select the name of any Google Group you manage.
4. From the navigation menu on the left side of the screen, select Group settings.
5. Go to Allow external members and select On.
6. Select Save changes.