https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages 

This article provides the basics: https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages You will find that Thunderbird does not have 'white lists' or 'black lists' to permanently identify spam, but relies instead on continual learning. That is, you need to periodically mark good messages as well as spam messages. If there are some spam messages that always come from an undesired email address, you can create a filter to force such messages to spam - or simply delete.