You can add or delete riskware detection custom policy rules for specified file extensions by using the Email Security - Server appliance Web UI or CLI:
When you add a custom policy rule for riskware detection on the appliance, email attachments or files with file extensions matching the specified extension are blocked or marked as custom riskware and excluded from further analysis.
Note
If you add a file extension to both a blacklist and a riskware rule, the blacklist takes precedence.