A global outage of Microsoft 365 began Thursday afternoon, knocking out Outlook email, Teams calendar functions and several AI‑powered services for users in multiple countries. Microsoft confirmed that an overloaded secure‑connection process caused a cascade of server failures, and despite deploying a patch early Friday, the service remained unstable, prompting further remediation efforts.

Scope of the disruption

According to Cointelegraph, the outage impacted Exchange Online, the backbone for Outlook and calendar data, preventing access to mailboxes for government agencies such as the U.S. Tenth Circuit Court of Appeals, Japan’s Finance Ministry and Singapore’s Government Technology Agency. CoinCentral added that schools, courts and businesses in the United States and Australia experienced similar interruptions, with Downdetector recording up to 140,000 Outlook outage reports at the peak.

Effect on AI integrations

Both OpenAI’s ChatGPT and Anthropic’s Claude rely on Microsoft 365 connectors to retrieve email and calendar information. The reports state that the outage caused most requests through these connectors to fail, prompting OpenAI to launch an investigation and Anthropic to acknowledge widespread failures in its Microsoft‑linked services.

Microsoft’s response and ongoing challenges

Microsoft posted multiple updates on X and its service‑health page, noting that a patch applied at 07:25 UTC improved stability on some servers but that restored servers could become unresponsive again as traffic rebounded. Engineers are exploring additional capacity‑increase measures, and administrators can track progress via incident IDs EX1550543 and MO1550821. The company emphasized that there was no evidence of a security breach.

What to watch next

Stakeholders should monitor Microsoft’s service‑health dashboard for further updates on the remediation timeline. Organizations that depend on Microsoft 365 for critical communications may consider temporary alternative channels, while AI providers are expected to publish detailed post‑mortems on connector reliability.

FAQ

When did the Microsoft 365 outage start?

The outage began around noon Eastern Time on Thursday, November 12, 2026.