Create a Filter List for a Modified Rule
When you modify a media type filtering rule to filter a different kind of media types, you also need to create a new filter list for use by the modified rule.
Select Policy | Lists.
On the Custom Lists branch of the lists tree, select Media Type and click Add.
The Add List window opens.
In the Name field, type a name for the new list, for example, Not Ensured Download Media Type Blocklist.
[Optional] In the Comment field, type a plain-text comment on the new list.
[Optional] Click the Permissions tab and configure who is allowed to access the list.
The Add List window closes and the new list appears on the lists tree under MediaType.
You can now fill the entries for the new list to let the media type filtering rule know what to block or allow.