What happens when you check the "Is Email Address" box on the "Configure Custom Attribute" page in the Symantec DLP Enforce Console?
Symantec/Broadcom Data Loss Prevention Enforce
When the "Is Email Address" box is checked, that custom attribute will appear as a checkbox in the To field in the "All: Send Email Notification" response rule action. This allows DLP admins to send the email notification to any custom attributes that are marked as email addresses.
Configuring the Send Email Notification action Broadcom tech doc