Yes! This is a very aggressive configuration and so it's not something that we typically recommend. However, there are cases where it makes sense.

Because the Approved Sender rules override all other filters, the easiest way to achieve this would be to create a custom filter rule that blocks "all" mail:

1. From within the control panel, go to Settings > Custom filters (shortcut link)
2. Add a custom filter rule like this:
   
   
   • For the first field, select Message header (any line)
   • For Condition, select Regex (Advanced)
   • For the search criteria Value use a dot followed by an asterisk (and no spaces):
     
     .*

   • Select either of these for when the rule has a match:
     • Quarantine
     • Quarantine, trash if spam

In the above example, the Quarantine, trash if spam option was used. Meaning, if an email is also identified as spam (by a core filter), it is marked as deleted spam. This might make it easier to identify senders that still need to be whitelisted since the quarantine hides deleted spam messages by default (and excludes them from emailed quarantine reports). There is, of course, an option to view deleted spam in the quarantine.