Late on 12 November 2026 (about 11:30 p.m. IST), Exchange Online failed worldwide. Outlook on web, desktop and mobile stopped sending and receiving mail, and Teams, OneDrive, OneNote, To Do and Microsoft 365 Copilot were hit too. Microsoft said there was no sign of a cyberattack. If you run IT for an office, the useful question is what your team should do in the first hour of the next one.

What Microsoft reported

  • A part of its server system came under very heavy load across many regions.
  • The trigger was not extra users. Several servers suddenly became unavailable and the rest were overloaded.
  • Restarted servers recovered briefly, then stopped responding under real traffic.
  • Reports say a fix was tested on a small group of machines and a recent network settings change was rolled back.
  • Incident IDs to track in the Microsoft 365 admin centre: MO1550821 and EX1550543.

First-hour runbook

  • Confirm on the official status page or the Microsoft 365 Status account on X before touching endpoints.
  • Tell users not to reset passwords or reinstall Outlook. A server-side fault cannot be fixed on the client.
  • Tell users not to resend mail. Queued copies may all be delivered when service returns.
  • Move urgent client contact to phone, WhatsApp or SMS.
  • Warn staff about fake support calls and phishing that ride on big outages.
  • Do not close the incident when one mailbox opens. Wait for Microsoft to confirm the fix.

Hardening for next time

  • A documented backup channel for the whole team.
  • A second email route through a different provider for urgent mail.
  • Your own backups of mail and files. The provider runs the service; protecting the data is on you.
  • A one-page outage plan naming who checks status and who informs clients.

More detail: full write-up of the Microsoft Outlook outage, with timeline and FAQs

Written by the team at Affix Center, an IT services company in Lower Parel, Mumbai.