Fun. Outlook failing to connect for multiple users... At least MS are aware: Current Status: We're investigating an issue in which some users may be unable to access or use Exchange Online services or features. We'll provide an update shortly.
And (allegedly) fixed again. Identical issue to yesterday, suggesting there may be some underlying issues with their infrastructure. I hope that they'll have implemented the fix without missing an important option this time (which is why it fell over twice yesterday, though I didn't tell you that).