Using School Buddy for Schools, you're able to send messages to and maintain an active contacts list. To learn more about what a contact is, check out the article linked here.
To view all of the active contacts for your school:
Make sure you're logged into a School Buddy account with proper admin permissions
Head over to the School Buddy for Schools admin panel
From the side navigation, choose the Contacts option. A list of all the active contacts for the school will now appear