System Setting for Emails Defaulting to Visible on Portal

In the cases section on the processing tab of the case page, you can click "hide email on portal" or "show email on portal" to control what portal users can see. But you can only do this after the email has been sent and is already on the processing tab. Currently there is no way to control if that email will default to hide or show. It would be nice to have a lookup or a system setting that lets you control: {if email meets this criteria, show/hide on portal}.