I've been trying to solve an issue with Outlook 2013 that started a few months ago.
My email has a folder named "Junk" (not Junk-Email). 95% of its contents are emails from my wife's Yahoo account.
I've added her to safe sender, safe recipient, whitelist, never block sender, never block sender's domain, never block sender's group; not in blocked list; no rules set. And yet all of her emails to my Sonic account get redirected from Inbox to Junk. Sometimes I get a glimpse of one in my Inbox and in a flash it's moved to Junk.