I spent a couple of days tearing my hair out. Word to the wise, if you are on bluehost and hit the Spam Experts trial (which I gather I did at some point). What happens is that when the trial ends, it silently queues all your mail into the spam experts and no mail at all flows into your domain.
You do not get any notice or warning and there is nothing on the console, but the good folks in tech support finally figured it out. Net, net, when you have a problem like this, then you want to make sure that all spam filters are off including the pay ones.
As an aside this blocked all mail on the inbound, so all forwards were also backed up silently./