Global Microsoft outage: Outlook, Teams down for 11 hours; what caused worldwide disruptions ?

PTC News Desk: Microsoft 365, Outlook, Teams and several other Microsoft services remained disrupted for more than 11 hours on Friday, affecting thousands of users. The outage also affected AI services from OpenAI and Anthropic that connect through Microsoft 365.

According to Downdetector, reports of Outlook problems reached a peak of around 1,38,058 at 1.30 am on Friday. The number later dropped to approximately 34,490 by 4.30 am.

Microsoft said its investigation found that a process responsible for creating secure connections on affected servers was getting overloaded. As a result, the servers were unable to handle user requests properly.

In a statement issued at 3.30 am on Friday, Microsoft said it was working to restore the affected servers and that services were gradually returning to normal as users reconnected.

Since the outage began, the company has shared more than 15 updates on X about its efforts to fix the problem.

In its latest update, Microsoft said it was increasing the capacity of its virtual machines to reduce pressure on its systems and restore services.

The company is also trying to repair servers that have stopped working properly by forcing them to sync with recent network changes. However, some servers are not syncing as expected, which is slowing down the recovery process.

Earlier, Microsoft said it was testing a configuration change on a small group of servers before applying it more widely. It was also restarting affected systems to bring services back online.

The company was also reversing a recent network configuration change that took place around the time the outage started to check whether it had contributed to the problem.

Microsoft temporarily restricted internet traffic in certain locations and began monitoring the affected servers to ensure they could operate properly before allowing more traffic.

The company clarified that the outage was not caused by an increase in user traffic. Instead, fewer servers were available to handle the normal volume of requests.

"We are aware and investigating reports of users experiencing issues with Microsoft 365 services, primarily issues with Exchange Online," a Microsoft spokesperson said.

The disruption affected several services connected to Exchange Online and Microsoft's email systems. However, features that did not depend on these services continued to work.

Which Microsoft services were affected ?

The outage affected several Microsoft products and services, including:

• Outlook and Exchange Online: Users faced problems accessing their email accounts through web browsers, desktop applications and mobile devices. Some emails were also delayed.

• Microsoft 365 apps: Users experienced difficulties accessing recently opened files.

• Microsoft 365 Admin Centre: Some pages failed to load.

• Microsoft Copilot: Users reported problems opening Copilot Chat and receiving responses through web and desktop applications. Access to work-related information, including emails, calendars and files, was also affected.

• Microsoft Teams: Basic messaging and online meetings largely continued to work. However, calendar access, meeting scheduling and some chat-related features were disrupted.

• Other services: Microsoft Planner, Microsoft To Do, Microsoft Defender, Microsoft Purview, Microsoft Graph, Microsoft Fabric, Power BI, SharePoint Online, Universal Print and Windows 365 were also affected.

Some Microsoft 365 Education services, including Assignments, Reading Progress and Speaker Progress, also faced disruptions. Certain Microsoft Intune services were affected as well.

Microsoft said services and features that did not depend on Exchange Online continued to function normally.

What caused the Microsoft outage ?

Microsoft initially blamed unusually high loads on parts of its infrastructure for the disruption. However, it later clarified that the problem was not caused by a sudden increase in user traffic.

Instead, a large number of servers unexpectedly became unavailable, putting additional pressure on the remaining working servers.

The company also found that problems with its automatic server health checks contributed to the outage. These checks are designed to monitor whether servers are working properly. However, some affected servers failed these checks and were taken out of service.

Microsoft also investigated whether a particular system component responsible for carrying out these health checks was contributing to the problem.

To fix the issue, the company began testing changes to its server settings and taking steps to prevent more servers from becoming unavailable.

Microsoft said it had found no indication that the outage was caused by a cyberattack.