Microsoft has published a Preliminary Post Incident Report on last week's events which broke Outlook on Windows for millions of users, making emails impossible to view or create.
It was on the evening of May 11th, UK time, and in the middle of the working day in North America (18:24 UTC, 19:24 BST, 11:24 Pacific), that many Office 365 customers using Outlook on Windows observed a frustrating problem: blank emails (or maybe showing just one line), even though a few lines of the email could be previewed in the list of messages. Attempts to create or reply to an email allowed a line of text to be typed, but when the user pressed enter, the text disappeared.
Admins steeped in the strange ways of Office and Windows tried the usual range of fixes, rebooting PCs, reinstalling Office, poking through the event viewer, digging deep into Outlook options to disable hardware graphics acceleration, but generally without success. The only things that typically worked was rolling back the last Office update, or running Outlook in safe mode. It was a huge waste of time.