Thunderbird email program does have a junk folder - {junk=spam}
if you go to -
tools, then options, then privacy tab
check your settings on those areas.
there is a show log button on that section too so you might click it and see what you find there.


[Cutting Out the Junk

Thunderbird's popular junk mail tools have been updated to stay ahead of spam. Each email you receive passes through Thunderbird's leading-edge junk mail filters. Each time you mark messages as spam, Thunderbird “learns” and improves its filtering so you can spend more time reading the mail that matters. Thunderbird can also use your mail provider's spam filters to keep junk mail out of your inbox.]
http://www.mozillamessaging.com/en-U...secure-protect

more help on the junk settings-
http://kb.mozillazine.org/Junk_Mail_Controls