I have had this problem many times. Suddenly emails I have received for months or years end up going to Spam. I keep moving them, hoping Mail will learn. Then it just stops happening. But it’s usually just not one email, it will usually be a few of them that it thinks are suddenly spam. So, I am of no help, other than to say I have had this happen many times over the years and it always just goes away on its own.
1 Like