Hotmail is silently destroying mail messages

I hate Hotmail. I really, really hate Hotmail. A few months ago one of my clients had problems with email being rejected by Hotmail. It seemed at the time just to be a bit of a scam to get people to sign up for their (expensive) implementation of the Sender Policy Framework, but by using a free SPF service, I was able to get things going again.

Fast forward to the present. Over the past few days, my client reports that a number of his clients with Hotmail accounts are simply not getting his messages. No bounce report, nothing. At first I'm quite skeptical that even Microsoft would just silently kill emails with no bounce report. But it seems I was wrong.

A lot of people are reporting just that. Microsoft's SmartScreen is silently killing emails, and tech support won't tell you why. Some people are reporting that email sent from Outlook gets through; other mail apps not so lucky. Sound familiar?

So is that SmartScreen, or We-just-can't-help-baiting-anti-trust-laws-Screen?