How to stop Apple Mail treating newsletters as junk?

I receive a couple of regular e-newsletters, but since the last OS update (which seems to have trashed all junk mail settings, even though they were working very effectively), they get treated as spam no matter how many times I add the sender to my contacts. I've checked the mail headers; they are always coming from the same sender, so it's not that it's changing all the time. This also happens with mails from some individuals, even though their addresses are in my contacts book and I both reply to their emails and create new mails addressed to them. I've tried tweaking all the junk filtering settings, but there aren't very many options to go at, and nothing seems to make any difference.

Has anyone managed to sort out the mess they've made of it and can offer any tip, please? I'm wasting so much time having to check the junk folder for genuine mails that the program's become virtually unusable.