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Outlook Email Disruptions Hit During Peak Business Hours

Microsoft said it is working to resolve technical problems that disrupted the ability of users to send and receive emails through Outlook, one of the most widely used enterprise communication platforms in the world. The issues surfaced during U.S. business hours, amplifying their impact across workplaces, schools, and public institutions that rely on Microsoft 365 for daily operations.

Outlook is a central component of Microsoft’s productivity ecosystem, which serves hundreds of millions of users globally. As reports of failed emails mounted, many affected users turned to social media to flag the outage and seek updates, highlighting how critical the service has become to routine communication.

Error Messages and Slowdowns Across Microsoft 365

Microsoft acknowledged the problem publicly at 2:37 p.m. ET, stating it was investigating an issue affecting Outlook. Users attempting to send or receive messages were encountering a “451 4.3.2 temporary server issue” error, a message typically associated with backend mail routing or server capacity problems.

The disruption was not limited to email. According to Microsoft’s service health dashboard, users also experienced degraded performance or failures across several other Microsoft 365 services. Search functionality in OneDrive was slow or unresponsive, while SharePoint Online and Microsoft Teams faced intermittent issues.

In Teams, some users were unable to create chats, schedule meetings, set up new teams or channels, or use features such as breakout rooms and live events. These tools are heavily used by businesses and educational institutions, compounding the operational strain caused by the outage.

Infrastructure Problems Identified in North America

By 3:17 p.m. ET, Microsoft said it had identified the source of the disruption. A portion of its service infrastructure in North America was not processing traffic correctly, leading to cascading issues across multiple applications.

Roughly an hour later, at 4:14 p.m. ET, the company reported that it had restored the affected infrastructure and begun rerouting traffic to alternative systems as part of its recovery process. These load-balancing measures are designed to reduce pressure on any single component of Microsoft’s vast cloud network.

Despite those steps, service availability remained inconsistent for hours. More than seven hours after the initial acknowledgment, some users were still reporting problems with email delivery and collaboration tools.

Gradual Recovery but Prolonged Degradation

Late in the evening, at 9:46 p.m. ET, Microsoft said it was seeing continued improvements as a result of its load-balancing efforts. The company noted that it was actively monitoring performance and making targeted adjustments to improve stability, while continuing recovery actions to ensure reliable service.

While Microsoft did not disclose the total number of users affected, the breadth of services involved suggests the disruption reached a significant portion of its North American customer base. Microsoft 365 is used by a large share of Fortune 500 companies, government agencies, and school systems, making even partial outages highly visible.

A Familiar Problem for Outlook Users

The incident revives memories of a major Outlook outage last July that lasted more than 21 hours, one of the longest service disruptions the platform has experienced in recent years. That event also affected email delivery and underscored the risks of dependence on centralized cloud infrastructure.

As Microsoft continues to expand its cloud services and integrate artificial intelligence features into its productivity tools, reliability remains a critical concern for enterprise customers. Frequent or prolonged outages can disrupt operations, delay decision-making, and erode trust, particularly for organizations that depend on Outlook as their primary communication channel.

For now, Microsoft says it is focused on restoring full functionality and preventing similar incidents. Customers and IT teams will be watching closely to see whether the company provides additional technical details or long-term measures to reduce the risk of repeat disruptions.

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