This changed in a later version of 12.1
Starting with Symantec Endpoint Protection 12.1 RU1 (12.1.1000.157), this setting has been moved.
The settings is now available in the domain properties of the Symantec Endpoint Protection Manager:
1. Open the SEPM Console
2. Select Admin on the left
3. Browse to Domains at the bottom
4. Right-click on the domain and select Edit Domain Properties