To add the attachment scan license:
In the Web UI, click the Settings tab.
Click Appliance Licenses on the sidebar.
Add the EMPS_ATTACHMENT_SCAN license that you received fromTrellix to your Email Security - Server appliance.
For information about adding an appliance license key, see the “License Management” chapter of the Email Security — Server System Administration Guide.
Click Email Policy on the sidebar.
Verify that "Attachment Enabled (uninstall license to disable)" appears in the Analysis Options section.