Also known as an exclusive whitelist, you can create and manage a list of trusted senders using the spam filtering whitelist and blacklist for a mailbox in the admin panel.

  1. In the list of mail accounts, click Modify for the account you want to configure.
  2.  Click Spam Control.
  3. Check the box next to SpamAssassin to enable spam filtering.
  4. Add your list of trusted recipients one per line in the “Whitelist From:”
  5. Add the following one entry in the “Blacklist From:” field:
  6. Click the Modify Email Account button.

What this does is blacklist mail from all addresses except those listed in the whitelist.