Users in a group can be divided into members and owners. These roles are used to determine which group permissions apply to a given user. If emailing a group is restricted to group owners, then users who are not owners of the group will not be allowed to send email to it.

Roles and permissions are a great way to restrict access for important communication channels to authorized parties. You can have groups where email is restricted to owners, owners and members, everyone in your domain, or everyone in the world. Try out the different settings. The following are the types of permissions you can set for a group:

1. Team (the default) - Email to this group is restricted to people in your school domain and individuals outside the domain who are members of the group. Useful for internal discussions, team discussions. Note that individuals outside the domain can be part of this group, so you could add parents or district staff who are not at your school to these lists.
2. Public - Email to this group is not restricted. Useful for contact lists from outside individuals, like alumni or parent communication. However, a public group might be prone to spam.
3. Announcement - Email to this group is restricted to people who are owners of the group. This is useful for internally broadcast top down communications, or for sending updates on a topic to a list of subscribers.
4. Custom - Restrict sending however you like.