Hi David, I believe In the majority of the cases the classification of "Junk or not" happens on your IMAP server and Thunderbird, just moves the messages in the appropriate folder. Thunderbird uses an adaptive filter that learns from your actions which messages are legitimate and which are junk. You can train it not to do that by using the approach listed here: https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages