Spam or Junk? Thunderbird's Junk Controls are NOT a blocklist. They use the frequency of word occurrences in your email to try to classify messages as bad or good. A great many bad messages have hidden swathes of text plucked from other sources (recipes, travelogues), raising the count of good words and so diluting the apparent frequency of bad words. The Junk Controls deliberately ignore the "from:" address as these are invariably spoofed in spam and junk messages. If you do have repeating messages from particular senders or with consistent subjects, you might consider using a filter to deal with them. But in general, filters are a poor way to mage spam/junk, since sensible spammers will do their utmost to be unpredicatble.