Since updating to Sierra 10.12.x and/or Mail 10.x, Mail seems incapable of learning what is not junk. I’ve seen forum threads outlining broadly similar problems, so it seems I’m not alone in this. What happens is that much more mail is being put into the Junk folder, put there by the Mail app itself (“Mail thinks this message is Junk Mail”). And most of it is not junk. So, I mark it as such. I can’t now use the old right-click method, because there is no longer an entry there for marking as not junk. Now I have to click the new “Not Junk” icon in the toolbar. So far so good, or at least that’s what I assumed. But Mail does not learn these “not junk” items. The same kinds of mail from the same senders are constantly being shunted into the Junk folder, even after I tell the app otherwise. I have tried some of the suggestions posted elsewhere here. For example, I tried a reset in Mail’s Preferences/Junk tab. Still the same problem. It seems from the other posts there is no cure for this … but if anyone does have any new suggestions I’d be pleased to give them a go. It’s very frustrating. I’ve just reported it to Apple.