This documentation only applies if you are using the Normal with Quarantine template for spam filtering.  If you are using other templates, your spam messages will not be quarantined in the spam folder.
To add quarantined senders to your whitelist follow these steps (the numbers on the arrow correspond to the step number):

  1. Click on Spam Management – it will expand as shown in the screenshot below after you click it.
  2. Click Quarantined Mail
  3. Put a check mark next to the message(s) which are legitimate mail  you want to receive
  4. Click the “Deliver selected messages normally” button.   The sender of the email(s) will be added to your personal whitelist, so that sender’s email will never be quarantined or blocked as spam again!