Your Message Notifications are set by default to daily. To change these settings for your domain, your domain admin needs to:
1. Log in as the administrator and go to the "Orgs and Users" Tab.
2. Go to "Orgs"
3. Go to "Notifications" (Bottom of page)
4. In the dark gray line, click "Edit"
5. Next to Spam, you may turn it off or change the frequency to every 2,3,4,5,6,7, etc. days.
6. Be sure to click Save.
These settings are on a domain level only. These settings may not be applied to users individually.