In the Admin Console, when you create an access policy the security options allow you to restrict external collaboration. Then you can override this permission by providing a 'justification'. However, the if you configure the access policy to 'block' specific domains or permit only specific domains, the 'justification' does not activate. I would like to see the user justification still be active. This provides a secondary reminder for the user that is going to be sharing the information to someone else.