If you're applying TB's Junk controls, contacts in certain address books can be whitelisted. But it's often more important to whitelist contacts at the mail provider's end, where mail may be marked as spam/junk/bulk before it's downloaded to TB. It depends on the mail provider, but in many cases it's sufficient to mark a message in webmail as 'not spam' or to add the contact to the webmail contacts list, which is different from the TB contacts.