These instructions are from a Mac ... but should work for you. Under the Thunderbird Menu Choose Preferences (May be called "Options" on Windows) In the Left Pane Click "Security" On the Top Tabs Click "Junk" Set it like in the Screenshot below. For about a month you're going to want to label mail that YOU consider junk with the "Junk" Button: so it can learn what to label as junk FOR You. (Or right click and choose from the "Mark" Menu ---> "As Junk" to flag it.) "Adaptive Junk Filter" included - just switch it on.