You would like to configure the Enforce Server to use SMTP over TLS to send out notifications and alerts.
Data Loss Prevention currently supports only non-TLS SMTP for reports and alerts being sent out from the Enforce Server.
A feature request is under consideration to address this issue in a future DLP release. As a workaround, the DLP administrator can configure the Enforce server to use a non-TLS SMTP server in DLP (under System -> Settings -> General) and configure this SMTP server to relay to a TLS enabled SMTP server for further delivery.
Configuring and troubleshooting SMTP relay issues (if any) will be outside of support scope.