Hold on to your inboxes, folks... best practices are no longer best — they’re required. Starting May 5th, Microsoft is cracking down on bulk senders who haven’t buttoned up their authentication, unsubscribe flows, and “Reply-To” game.

In this post, I break down what Microsoft’s new sender requirements actually mean, how they compare to Google and Yahoo’s standards, and what to fix before your emails start getting flat-out rejected.