Cloud

Microsoft Blames Daylong 365 Outage on a Flaw From an Earlier Network Capacity Upgrade

Outlook, Teams, SharePoint, Copilot and Defender were disrupted for close to a day across dozens of countries. Microsoft apologized, said the cause was 'not related to cyber or AI / agents' and promised a full post-incident report.

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Microsoft Blames Daylong 365 Outage on a Flaw From an Earlier Network Capacity Upgrade
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Illustrative photo of hands typing on a laptop surrounded by drawn envelope icons; it does not show Microsoft software, a Microsoft data center or the outage. The keyboard uses a German-style layout. No company logos are visible.

Microsoft said on Friday that the outage that knocked out Outlook and other Microsoft 365 services for close to a day grew out of "an issue during an earlier network capacity upgrade," and apologized to customers and partners as service gradually returned. The company said the underlying problem had been addressed and that it was still restoring service to remaining customers and regions.

"We are deeply sorry for the disruption this incident has caused our customers and partners. We know the trust they place in our services and take that responsibility extremely seriously," a Microsoft spokesperson said, according to CNBC. Microsoft has promised a full post-incident report once its review is complete.

At a glance

Item Detail Source
Start Shortly before 1 p.m. ET Thursday, Nov. 12 (about 10 a.m. PT) CNBC
Services hit Exchange Online/Outlook, Teams, SharePoint, Microsoft 365 Copilot, Defender, Intune Moneycontrol; TechCrunch
Reach Problems reported in at least 74 countries BBC
Duration About 18 hours of downtime before traffic returned, per Kentik TechCrunch
Stated cause Issue from an earlier network capacity upgrade, surfaced by a later network change Microsoft via Moneycontrol
Malicious activity Microsoft says none; "not related to cyber or AI / agents" Microsoft via TechCrunch

How it unfolded

CNBC reported that connectivity problems began shortly before 1 p.m. Eastern time on Thursday. The problems were first flagged as affecting services in the United States and the Americas, then spread around the world as engineers struggled to recover downed servers, TechCrunch reported.

Microsoft's early updates described infrastructure under "elevated load across multiple regions." It later said the load was not caused by more traffic but by "a number of servers being unexpectedly unavailable; straining the remaining infrastructure," CNBC reported. Some servers were failing automated health checks. At 4 p.m. ET Thursday, Microsoft said it had "validated an alternative service health check method" that brought some servers back and that it was preparing automated systems to detect and restart unresponsive servers.

Those fixes did not hold everywhere. Moneycontrol reported that earlier recovery attempts, including server restarts and traffic rerouting, produced partial gains that faded. Outlook and other Microsoft 365 tools were largely down through the Asian and European business days and into Friday morning in the United States, according to CNBC. Microsoft said around 10:30 a.m. ET Friday that it was seeing "encouraging recovery progress," with email delivery improving.

Doug Madory, director of internet analysis at the network monitoring company Kentik, said in a Bluesky post that traffic was returning after about 18 hours of downtime, TechCrunch reported.

What Microsoft says went wrong

In a statement posted on X on Friday, Microsoft traced the incident to an issue introduced during an earlier network capacity upgrade that came to the surface after a more recent network change, Moneycontrol reported. The company called it "a technical issue not related to cyber or AI / agents." Its status page had earlier said only that it was not aware of malicious activity.

Microsoft's earlier updates also described a secure-connection process becoming overwhelmed on affected machines. Prof. James Ferryman of the University of Reading's computer science department explained to the BBC why that kind of fault is slow to fix: once one server falls over, its work moves to the next, while huge numbers of phones and laptops keep trying to reconnect. "You can't just turn it all back on at once. You have to bring it back bit by bit," he said.

Microsoft said it restored services in stages and checked stability at each step, acknowledging that this lengthened recovery, according to Moneycontrol.

Who felt it

The BBC reported disruption to schools, healthcare systems, businesses, courts and governments. Britain's National Health Service said some services were affected but told patients to attend appointments as normal, CNBC reported. Courts from Los Angeles to Texas warned that communications could be delayed, and Japan's government said its shared IT platform was disrupted, according to the BBC. OpenAI said it was investigating a problem with its connections to Microsoft's services.

Companies felt it too. CNBC reported that Swiss luxury group Richemont's earnings were slightly delayed, and that electric truck maker Workhorse moved its third-quarter results from Nov. 12 to Nov. 16. Air India said it temporarily rerouted emails so it could keep receiving customer messages.

Downdetector logged nearly 130,000 problem reports for Outlook at the peak, Moneycontrol reported; the BBC cited a peak of nearly 140,000 on Thursday. Microsoft has not confirmed how many of the more than 430 million people it says use Microsoft 365 apps were affected.

Will delayed email arrive?

Microsoft extended its email timeout window to 48 hours "to help protect delayed messages as delivery catches up," the BBC reported. Messages that arrive late carry the time they were delivered, not the time they were sent. Microsoft warned that some users may still see intermittent access problems and delayed delivery as queues clear.

Why it matters

The outage follows another major incident in September, when a days-long disruption of Microsoft's cloud services was blamed on a "core authentication configuration" issue, TechCrunch noted.

Former Skype and Uber engineer Gergely Orosz told the BBC this could be the "most disruptive" business email outage "of all time." James Owen of the consultancy Control Risks told CNBC it exposed a "resilience and dependency issue that has been decades in the making," and urged organizations to plan for manual backups, offline procedures and more diverse suppliers. Rep. Josh Gottheimer, D-N.J., told CNBC he had asked for a briefing.

For IT teams, the practical lessons are familiar but sharper: know which business processes stop when email and identity-linked services go dark, keep a non-Microsoft channel for urgent communication, and read Microsoft's post-incident report closely when it arrives. The key open question is why a flaw from an earlier upgrade went undetected until a later network change set it off.

How we reported this

DailyMech read reports from TechCrunch, CNBC, the BBC and Moneycontrol in full. Microsoft's status page and X posts were not read directly; Microsoft's statements are quoted as those outlets reported them. The cause described here is Microsoft's preliminary explanation. DailyMech contacted no one for this article.

Published November 13, 2026. Facts checked against the cited sources by DailyMech's AI writer.

Sources

DailyMech used AI tools to research and draft this article. Facts were checked against the cited sources by DailyMech's AI writer, not by a human editor.

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