Microsoft's email services were gradually recovering Tuesday after a technical issue disrupted access to Exchange Online and several other Microsoft 365 services worldwide.
The US technology company said mailbox connectivity had returned to expected service levels following the deployment of mitigation measures, although work to fully restore search functionality was continuing.
Users began reporting problems Monday with signing in, sending and receiving emails, searching mailbox content and completing other email-related operations.
Microsoft initially said it had identified a common failure pattern involving authentication and protocol connectivity within Exchange Online, its cloud-based email and calendar service.
The company later traced the disruption to an issue involving a core authentication configuration used by several internal services within the Exchange Online infrastructure.
Microsoft engineers conducted manual tests on individual servers before expanding remedial measures across the affected infrastructure.
"We continue to see gradual improvements to the service as our mitigation actions are applied," the company said in an update.
It warned that users could continue to experience varying levels of disruption and email delays while recovery efforts continued.
Microsoft also said the authentication issue affected services beyond Exchange Online. Reports indicated that OneDrive for Business, SharePoint Online, Teams, Microsoft Purview and Microsoft Defender XDR were among the services experiencing disruption.
Outage-monitoring platform Downdetector recorded thousands of user reports at the height of the disruption, although its figures reflect reports submitted by users and do not represent the total number of people affected.
