Microsoft revealed the root cause of the massive outage that lasted for hours.

Microsoft has disclosed that the worldwide outage of Microsoft 365 that occurred earlier this week was caused by a power outage in the infrastructure, which in turn caused failovers in traffic management services in multiple regions.

The company received a wave of sudden complaints from their users reporting multiple problems.

This includes severe difficulties logging into their Exchange Online mailboxes as well as sending emails from those mailboxes.

The Microsoft 365 outage occurred at the same time as a widespread service outage that had been affecting Cloudflare since early Tuesday morning.

Microsoft 365 Outage

Microsoft customers began experiencing and reporting a variety of issues on Monday, June 20, at 11:00 PM UTC, when they attempted to access and use Microsoft 365 services.

According to Microsoft, customers who tried to access certain Microsoft 365 services during the incident experienced various issues, including delays and failures.

The company confirmed the problem in a tweet stating, "We're investigating an issue in which some users are experiencing delays or connection issues when accessing the Exchange Online service. Please see EX394347 in the admin center for more information."

In addition, customer reports disclosed information regarding persistent requests to re-login, the failure of e-mails to be delivered after becoming stalled in queues, and an inability to access Exchange Online mailboxes despite utilizing all of the available connection methods.

Users who were affected by the outage also reported experiencing delays or errors when using the search and calendar functions provided by the affected services.

The Microsoft Teams communication platform, Universal Print, the Exchange Online hosted email platform, Graph API, and SharePoint Online are some of the services that have been impacted by this outage.

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Microsoft's Outage Lasted for 16 Hours

Microsoft's current outage is stated to have lasted for hours.

According to BleepingComputer, "More than 16 hours after the first signs of the outage were detected, on Tuesday, June 21, at 3:27 PM UTC."

As reported, Microsoft's customers were effectively kept in the dark despite the fact that Microsoft assured them they could obtain additional information regarding this incident from the admin center under the tickets EX394347 and MO394389.

This is despite the fact that Microsoft informed customers that they could do so.

According to an email sent by Microsoft, "We've confirmed from our updated service monitoring that all services remain healthy following the targeted restarts."

The company added, "Additionally, we completed our investigation into the potential remaining impact to Outlook on the web and confirmed that this is a known issue which is unrelated to this event."

Microsoft's 365 outage severely impacted western Europe. On the other hand, users from North America, the Asia-Pacific regions, Europe, the Middle East, and Africa also experienced the outage.

An infrastructure power outage was reported to be the root cause, which forced a failover to Microsoft 365 traffic management to continue providing service to customers, most of whom were located in Western Europe.

This action was unable to be finished, which resulted in delays in functionality and access failures for a number of services provided by Microsoft 365.

Most of the outages and malfunctions of Microsoft products have so far been resolved.

However, as of writing, Microsoft's portal shows that problems and issues while using Outlook.com could still be experienced.

Furthermore, the company also promised that a post incident report will be published within five business days.

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