Details of the Hotmail / Outlook.com outage on March 12th

Outlook.com left preview a few weeks ago, and as part of that, we shared that we'd start to upgrade the hundreds of millions of people using Hotmail to the new, modern Outlook.com experience. We had done multiple pilots during the preview period and learned a ton. Overall, the upgrade has been going very well - people have upgraded much faster than we had expected. The vast majority of people using our services have had a smooth experience during this time and are enjoying the new Outlook.com experience. That said, we had an issue yesterday and wanted to provide you with a deeper look at what happened.