You want to know if an SMTP Email Client is installed with the Network Prevent for SMTP as you see traffic on TCP port 25.
No, A SMTP Email Client is not installed with the Data Loss Prevention product.
The ports used by the Network Prevent for SMTP are configurable, the default ports used are 10025 for the Upstream MTA and 10026 for the Downstream MTA but we recommend using port 25 where possible.
For more information on configuring the Network Prevent for SMTP please refer to your DLP documentation Administration guide and Email_Prevent_MTA_Integration_Guide.
References:
Data Loss Prevention SMTP Prevent Diagnostic and troubleshooting