A broad Microsoft outage disrupted Outlook email and other Microsoft 365 services on Thursday, leaving many people unable to open their work mailboxes while the company shifted traffic across its global network to ease the strain. Microsoft said the problem was still being fixed as of 2:40 p.m. ET, and it has not said when service will be fully back to normal. This is a developing story.
Microsoft confirmed the email failure shortly before 1 p.m. ET on its Microsoft 365 Status account. “We’re investigating reports of users experiencing issues accessing Exchange Online mailboxes through multiple connection methods in the Americas,” the company said, pointing administrators to incident EX1550543 in the Microsoft 365 admin center. Exchange Online is the system that runs Outlook email for businesses, schools and government offices.
The failure could hit every route into a mailbox: Outlook on the web, the Outlook apps, and the connections other mail programs use, which Microsoft lists as MAPI, Exchange ActiveSync and REST. In its service health notice, Microsoft said: “Users may be unable to connect to their mailboxes in Exchange Online through multiple connection methods.” It added: “We’ve identified connectivity errors occurring on a portion of Exchange Online infrastructure which receives and processes users’ access requests. We’ve collected networking logs to review to further investigate the source of these errors and confirm our next steps.”
Within the hour, Microsoft widened the warning. “While we’re working to mitigate impact, we’ve confirmed the issue may affect Microsoft 365 service connectivity for users in any region,” the company said in a post at 1:07 p.m. ET, and it opened a broader advisory, tracked as MO1550821. It then reported its first finding: “We’ve determined a portion of infrastructure is experiencing elevated load across multiple regions, which is likely contributing to the connectivity errors.”
To relieve the pressure, Microsoft said: “We’ve begun redistributing connection traffic across our broader worldwide infrastructure to help balance the load.” In a later notice, Microsoft said it was also restarting and repairing the affected parts of its infrastructure to restore capacity, and it warned that shifting traffic could cause delays for some users. The company has not explained what pushed the load up, and it has not given a root cause. Its service health notices promised further updates during the afternoon.
The scale showed up first in user reports. Downdetector, which tracks outages by collecting reports from users, recorded more than 130,000 reports of problems with Outlook at 1:27 p.m. ET, according to Reuters, after reports began surging around midday. It logged more than 46,000 reports for Microsoft 365 and about 3,000 for Teams. Those numbers count reports, not confirmed affected users, and the real number of people affected may be different. Downdetector also drew thousands of user reports for OneDrive, Copilot, the Microsoft Store, Azure and Xbox, but Microsoft has not confirmed problems with those services.
The email outage was the second Microsoft failure of the day. Earlier on Thursday, Microsoft investigated trouble with Teams in North America under a separate incident, TM1550488. “We’re investigating reports of users experiencing issues when accessing or using Microsoft Teams functionality in North America,” the company said at the time. Microsoft later said the Teams problem was fixed and its impact fully resolved, even as some users kept reporting trouble.
For now, there is little for affected users to do but wait. Administrators can follow incidents EX1550543 and MO1550821 in the Microsoft 365 admin center or on Microsoft’s public status page at status.cloud.microsoft. Zark News will update this story as Microsoft posts new information.
