Email problems: hours-long disruption to Microsoft's cloud email service

A prolonged outage caused many businesses and consumers to lose access to Microsoft's cloud offerings, including the email service Outlook. The disruption affected a wide range of services from the tech giant. For instance, when it came to the business communication tool Teams, tasks that relied on calendar integration failed. For corporate clients, the AI assistant Copilot was also unusable.

Microsoft documented its battle against the failures on the online platform X, but initial attempts did not yield success. The company initially reported issues with Exchange-Mailboxes in the United States. Then, it emerged that the outage might affect users worldwide on Microsoft 365. Efforts were made to reroute data traffic away from possibly problematic servers.

Microsoft claimed a breakthrough when a process that crippled affected servers was discovered. It then announced that it would bring some servers back online, but they remained stable as long as data traffic reached them. An hour later, the engineers were disappointed again: the servers could go down again as soon as traffic reached them, according to Microsoft engineers.

In its next attempt, the company tried to isolate parts of the infrastructure and saw "positive results," it said. Microsoft had to concede defeat shortly after: the measures did not work as expected. The duration of the disruption remained unclear. Outages of online services are common, but sometimes they are so severe or so difficult to pinpoint that they lead to hours-long outages.

Microsoft's email services had already experienced a similar hours-long outage as recently as late August, when users could not log in or send and receive messages for hours on end. Microsoft cited an issue in the cloud infrastructure as the cause.