I've been having a problem for a few months of spam getting into my inbox. Thunderbird knows it's spam because it marks it as such. But it does not move it or delete it. I actually have a message filter to delete spam and it doesn't seem to be doing anything.

I was also getting this kind of spam despite having another layer of deletion on my POP server yellow mail (I have marked a few addresses as "RED" and to delete them from the server and yet they still get through my email account AND sit there in my Thunderbird inbox with a "fire sign".)