Well I see you have a load of opinions aboput what Thunderbird should do, buyt have not turned off the junk controls in Thunderbird in settings. Once you do that Thunderbird will do nothing with junk. It will not even look at it. So perhaps make the setting change. https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages Now if you issue continues after junk processing it turned off in Thunderbird (and I expect they will) it is not Thunderbird that has done the placements or the decision making. The fact that there are no real definitions or agreed method for dealing with SPAM makes it complicated. Most third parts antivirus programs have some sort of antivirus scam/spam tool that does an appalling job of managing spam. Sometimes mail is just deleted it outright, sometimes it puts mail in a spam or junk folder. Trend had a particularly egregious tool at one point. But i have over a decade of reading about the many failings of Antivirus products. Usually the issue is blamed on Thunderbird by folk that do not realize they have this antivirus tool making a mess of things. These days most folk also configure their mail accounts as IMAP so they get all their server side folders, and every provider I have seen has some sort of spam filtering of their own. Usually this is something you can not opt out of and they are particularly good at filing family mail as SPAM. The Yahoo bulk mail one will even keep putting the same email back in SPAM even after you move it somewhere else and say the mail is not spam.