Microsoft said Friday that a bug introduced during a network capacity upgrade caused a worldwide outage across its workplace services, including Outlook.
The company said it had fixed the underlying problem and was bringing remaining customers and regions back online in stages. The gradual recovery took longer, Microsoft said, but allowed it to check that services were stable along the way.
Microsoft ruled out a cyberattack and said the outage was not caused by interference from AI agents. It plans to publish a fuller explanation after completing an internal investigation.
The company apologized to customers and partners, saying it was seeing broad recovery and greater stability across its services.
Some Outlook users began regaining the ability to send and receive messages Friday morning. The disruption started Thursday afternoon and affected Exchange Online, the system that supports Microsoft’s email services, disrupting businesses and users around the world.
In updates posted early Friday, Microsoft reported improvement in Europe and Asia Pacific, with Japan comparatively stable. Service in North America was also getting better, though the company warned that some users might continue to encounter intermittent problems.
To protect delayed messages, Microsoft extended its email delivery timeout to 48 hours. Ordinarily, a message that cannot be delivered within the standard period is returned to its sender. The extension gives messages held up since Thursday afternoon until at least Saturday afternoon to reach their recipients.
Outlook problems extended beyond email. Users reported trouble viewing calendars, sending meeting invitations and changing existing events. Some people also couldn’t access recently used files in Word, Excel and PowerPoint, while external file sharing in SharePoint Online was affected.
Microsoft’s Copilot assistant was also disrupted. Users reported being unable to load chats, get responses or retrieve information from their emails, calendars and files.
The outage affected businesses as well as individuals. Indian airlines IndiGo and Akasa Air reported issues with customer-support email, while Air India temporarily redirected its email services.
OpenAI and Anthropic also reported problems with tools connected to Microsoft 365 on Friday morning. Both companies said later in the day that the issues were beginning to ease.
