You can choose to turn off domain access notification emails. (For more information about Domain Access, go here.)
This feature lives in the Domains & Publishing section of the dashboard. To access it:
1) Click on the pencil icon to edit the domain settings
2) Scroll down to the Access section
3) To opt in to receiving access notification emails, check the box. To opt out, leave the box unchecked. (Note: The "Receive notification on initial access" box will display regardless of the domain access level selected.)
4) Select "Save Access Settings" to apply change.