One outage, millions affected. What went wrong at Microsoft?

On November 12, Microsoft’s email service, Outlook, began experiencing widespread failures, marking the start of a major disruption that would affect millions across the globe. The issue continued into the following day, Friday, November 13, highlighting the far-reaching consequences of a single service failure. Exchange Online, the back-end server responsible for managing user data, was the root cause of the issue.

Users found themselves unable to connect to their mailboxes through various connection methods. Microsoft Exchange Online and Microsoft Outlook, the front-end app used to interact with the data, were both impacted.

Microsoft’s incident tracking system, MO1550821, was used to publicly record the ongoing service degradation and outage. The disruption started at 6.26 pm UTC on Thursday, or 11.56 pm Indian Standard Time (IST). Initial reports came from the Americas, but Microsoft quickly warned that any region could experience the issue. By Thursday afternoon, Downdetector, a platform tracking online service disruptions, recorded over 130,000 reports of Outlook problems in the United States.

In India, complaints began shortly before midnight and reached 2,157 by 11.42 pm. Reports rose again to 1,960 by 8.42 am on Friday as people began their workday.

Microsoft’s explanation for the outage evolved as more information became available. Initially, it stated that several servers had unexpectedly become unavailable, causing an increased load on the remaining infrastructure. However, it was later revealed that a process responsible for establishing secure connections had become overwhelmed, leading to servers halting request handling.

Microsoft also mentioned that a recent network configuration change correlated with the start of the incident. Despite earlier updates claiming no recent change was linked to the problem, recovery efforts were complicated by servers becoming unresponsive as traffic was restored.

Microsoft attempted to resolve the issue by restarting and rebuilding affected servers, restricting certain types of traffic, rerouting connections, and improving capacity. However, the challenge was not merely to bring servers back online but to ensure their stability as traffic returned. Microsoft clarified that it had no evidence suggesting malicious activity caused the outage. The precise root cause remained unconfirmed, and the company committed to publishing a post-incident report.

The wide-ranging impact of the outage extended beyond Microsoft. Other Microsoft 365 features, such as Copilot for Microsoft 365, Teams, Planner, To Do, Defender, Purview, Power BI, and Microsoft Graph, were also disrupted. This affected public institutions, including the Australian government bodies, Japanese government IT infrastructure, and users in the US House of Representatives.

Additionally, Indonesian airline IndiGo and Indian airline Akasa Air reported email-support service disruptions. The effects reached financial firms in Taiwan and even sparked humor and frustration on social media as users joked about skipping meetings and taking the day off.