We need to "Mark-Not-Junk" or to edit the "Spam" or "Junk" message filter by each address or Subject. It is tedious to go through the Junk folder multiple times for an address that inadvertently got marked Junk.
Did you read how the address book acts as a white list for Junk filtering, so putting the email address in your address book and flagging it in account settings as a whitelisted address book means that address will never goto junk again.
It does not however affect your provider's spam filtering. Almost everyone I have seen in support in years with overly aggressive SPAM filtering problems has had an issue with their provider's spam filter, not Thunderbirds.