Parental controls for iCloud Mail

I am trying to set up an ipad that uses the latest ScreenTime settings in iOS13.4 and this works perfectly for limiting iMessage and FaceTime to known contacts only - from a parental control perspective, its actually very good.

I am now wanting to do the same with iCloud Mail, that is limit inbound and outbound messages to known contacts only, with everything else being rejected or quarantined for adult approval/rejection.

If I cannot achieve this 'out of the box' with iPad and iCloud could I have some recommendations on how to secure/lock down email (ideally still using iCloud Mail so that the contact address is the same for Messages and Mail).

Many thanks.