Symantec Endpoint Protection Manager sends out more than one "Risk Outbreak" email notification for each risk detection.
12.1 RU5
Previously processed window events are processed in next window due to last triggered time not getting updated properly.
This problem is fixed in Symantec Endpoint Protection 14. For information on how to obtain the latest build of Symantec Endpoint Protection, read Download the latest version of Symantec Endpoint Protection