Rated 5 out of 5 stars

by David on Sept. 29, 2015 · permalink

Initially I had the same problem as fgilbert, my folder was named "Unerwünscht". The solution Alex Cabal suggested was to go to
Account Settings -> [Account] -> Junk Settings -> Destination and Retention
and set Thunderbird to move new junk messages to the folder in question. Now it works exactly as advertised. Thanks again!