The automatic reported Incident emails can be turned off via Settings > Company Edit > System Settings > disable the 'Send Incident Notification Emails' toggle> and click Save. 

You may want to use this setting if custom Incident email notification rules have been created via the Incident Rulebase. See the articles below for more information:

• What does Incident Rulebase do?
• Incident Rulebase - How do I create a Rule & Actions?
• Incident Rulebase - How to activate Incident Rules?
• Incident Rulebase Auditing