This policy setting allows you to configure the list of moderate risk file types. If the attachment is in the list of moderate ...

This policy setting allows you to configure the list of moderate risk file types. If the attachment is in the list of moderate risk file types and is from the restricted or Internet zone, Windows prompts the user before accessing the file. This inclusion list overrides the list of potentially high risk file types built into Windows and it takes precedence over the Low risk inclusion list but has a lower precedence than the High risk inclusion list (where an extension is listed in more than one inclusion list.)

If you enable this policy setting you can specify file types which pose a moderate risk.

If you disable this policy setting Windows uses its default trust logic.

If you do not configure this policy setting Windows uses its default trust logic.