WASHINGTON, D.C. — A widespread Microsoft Outlook outage that began around 1 p.m. ET on Thursday disrupted email, calendar, Teams meetings and OneDrive access for an estimated 400,000 enterprise customers across the United States, prompting emergency response plans at corporations, school districts and municipal offices.

The outage, which Microsoft confirmed lasted roughly 18 hours before Outlook services began to stabilize on Friday morning, coincided with the start of the U.S. earnings season. Analysts at Bloomberg noted that the disruption hit roughly 30 percent of public‑sector institutions that rely on Office 365 for daily operations, raising short‑term productivity concerns for firms that reported quarterly earnings on Thursday.

Corporate leaders described the impact as “significant but manageable.” “We rerouted critical communications through alternate platforms and activated our business‑continuity protocols,” said Karen Liu, CIO of a mid‑size technology firm in Austin, Texas. The incident also prompted a brief dip in Microsoft’s stock, which fell 1.2 percent in after‑hours trading on Thursday, though the share price recovered after the service began to resume.

Local governments reported varying levels of service loss. Miami Mayor Francis Suarez warned that the city’s 311 call center experienced a three‑hour delay in responding to non‑emergency requests. In Maryland, the Department of Transportation said its scheduling system for road‑work permits was offline for six hours, while Los Angeles County officials indicated that school district staff could not access shared documents, delaying the distribution of summer‑break schedules.

Microsoft’s senior vice president for cloud operations, Scott Guthrie, told reporters that the company identified a “routing anomaly” in its data‑center network and deployed a “global fail‑over” within two hours of detection. He added, “We are working around the clock to restore full service and to implement additional safeguards that will reduce the likelihood of a repeat event.” The firm also offered a credit program for affected enterprise customers.

Key Takeaways

• Outage began at 1 p.m. ET Thursday and lasted about 18 hours before Outlook services resumed.
• Approximately 400,000 enterprise customers, including 30 percent of U.S. public‑sector users, were impacted.
• Microsoft attributed the disruption to a routing anomaly and pledged network‑redundancy upgrades.

As Outlook returns to normal, businesses and government agencies are reviewing contingency plans to mitigate future cloud‑service interruptions, while investors watch Microsoft’s upcoming earnings release for signs that the outage has not caused lasting financial damage.