Email in Junk folder not marked as Junk

Thanks for the reply, but that doesn't make sense to me. Why should it not assume that new mails in the Junk folder should be considered Junk? To some degree it correctly does assume that it is Junk, b/c it refuses to let me mark them as Junk, I can only "mark as not Junk & move to Inbox".

I don't want to disable the Junk filter of my mail provider, because it works quite well. Also if I would rely only on Apple Mail's Junk filter, that wouldn't work if the machine is not running, and I would get Junk mail in my phones Inbox. I get around 100 Junk Mails per day.

All I want is that external content is not loaded when I quickly browse through those mails to check for false positives and thus also mark them as "read". To me that doesn't sound unreasonable, or does it?

I'm pretty sure this worked quite well before the Catalina upgrade. I.e. mail in the Junk folder was correctly marked as Junk even with the mail provider's filter enabled. Only sometimes was there the odd Junkmail not properly marked in the Junk folder. I was on Sierra up until recently. Not sure what changed...

Thanks. I see your point, however I disagree with this design decision. IMHO it would not at all be unreasonable for Mail to assume everything in the Spam folder is meant to be Spam and should be used to train the filter, regardless of how it got there. Mails that are classified by Apple Mail as Spam automatically are also treated in the same way as those that I manually mark as Spam.

But regardless, even given how it treats these messages, it's still not reasonable that I can't then manually mark them as Spam directly inside the Spam folder, without first moving them out of the Spam folder. And not loading external images should also be done for all messages in the Spam folder, regardless of "marked as Spam" status.

I disabled my provider's Spam filter and it seems like the reason the behaviour appears to have changed is that Mail's Spam filter now detects 0% of those ~100 Spam messages I get per day as Spam. It seems like this might have changed during the Catalina upgrade. Of course I reenabled my mail provider's Spam filter.

I have already tried to reset Mail's Spam filter and have now manually marked the emails from the past few days after the upgrade as Spam, but the filter hasn't yet started to pick them up. To me as a human they appear very repetitive and distinct. Is there something more I can do other than to the "Reset" button in Mail's preferences? Could this be some strange artefact from Sierra -> Catalina upgrade?