TLDR

  • Microsoft Outlook crashed Thursday afternoon, preventing users from sending or receiving emails with “451 4.3.2 temporary server issue” errors starting at 2:37 p.m. ET.

  • Over 15,890 users reported problems at peak, with OneDrive, Teams, SharePoint, Microsoft Defender, and Microsoft Purview also experiencing disruptions.

  • Faulty North American infrastructure caused the outage, which lasted more than seven hours before Microsoft restored services Friday morning.

  • Microsoft rerouted traffic to alternate infrastructure and performed load-balancing to fix the issue affecting businesses, schools, and government offices.

  • By 1:05 a.m. ET Friday, incident reports dropped to 113 as Microsoft confirmed all affected infrastructure was healthy again.

Microsoft battled a major Outlook outage Thursday that knocked email services offline for thousands of users during critical business hours.

The problems began at 2:37 p.m. ET. Users trying to access email received “451 4.3.2 temporary server issue” errors. The disruption hit schools, companies, and government agencies across the country.

Microsoft acknowledged the crisis on X. The tech giant confirmed issues affecting Outlook and several other Microsoft 365 applications.

#BREAKING Microsoft is experiencing a major outage right now!

Thousands of users are reporting issues with Microsoft 365 services, including:
– Outlook (email sending/receiving blocked, error codes like 451 4.3.2)
– Teams
– Exchange
– Microsoft Defender
– Microsoft Purview
– And… pic.twitter.com/npcBnvcMbm

— Breaking News (@TheNewsTrending) January 22, 2026

The outage spread beyond email. OneDrive file searches slowed to a crawl or stopped working entirely. Teams users couldn’t create meetings, chats, or channels.

SharePoint Online collaboration tools also went down. Microsoft Defender and Microsoft Purview joined the growing list of broken services.

Downdetector recorded the damage. More than 15,890 users flooded the site with complaints at the outage’s peak.

North American Infrastructure Fails

Microsoft identified the problem by 3:17 p.m. ET. A chunk of North American service infrastructure wasn’t handling traffic properly.

The company started shifting users to backup systems. Engineers worked to restore the failing infrastructure while balancing loads across healthy servers.

At 4:14 p.m. ET, Microsoft announced it had fixed the broken infrastructure. The team redirected traffic to functioning systems to speed recovery.

But normalcy didn’t return quickly. Services stayed degraded well past 9:00 p.m. ET, more than seven hours after the initial failure.

Slow Path to Recovery

Microsoft posted updates throughout the evening. “We’re seeing continued improvements in service availability and functionality as a result of our load-balancing efforts,” the company said at 9:46 p.m. ET.

Engineers monitored performance and tweaked settings to stabilize systems. The recovery process stretched into Friday morning.

Social media filled with frustrated users. The outage exposed how reliant organizations have become on Microsoft’s cloud infrastructure.

Friday brought relief. Microsoft declared all services restored and infrastructure healthy.

Downdetector confirmed the turnaround. Incident reports crashed from over 15,890 to just 113 by 1:05 a.m. ET.

Microsoft successfully rerouted traffic back to repaired infrastructure. The company resolved impact across all affected Microsoft 365 services after hours of emergency repairs.

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