Do you have contacts that you don't want to send penalties too?
To achieve this is quite simple, any 'group' which has no policies applied to it, will effectively become a whitelist.
So to do this, Create a group and add contacts to it using the search bar. Do not assign any policies to this group.
(You cannot use the default group as contacts cannot be added to it)
That's it! Now members of this group will not have any invoices processed.
Important note: If you remove the contact, delete the group, or assign a policy to the group. Then all the contacts in the groups previous invoices will be processed.