This is how the Thunderbird junk filter works: https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages Thunderbird tends to use the word 'junk', though 'spam' is also used generally. I've no idea why you have both folders, it's possible that your email provider also has a spam filter working on your account. I assume of course that it's sPam you are writing about, not sCam (since Thunderbird has a scam filter too).

I have this problem/question too. Sheesh, it's not easy finding/getting into Mozilla's forums is it?!?