If Outlook wouldn't open yesterday afternoon, or your Teams calendar went blank, it wasn't you, your Wi-Fi or your laptop. Microsoft 365 has had a significant outage, and at the time of writing on Friday morning Microsoft's engineers are still working to restore full service.
Outages on this scale are rare for Microsoft 365, and Microsoft has kept customers updated throughout the night. Here's what happened, what still works, and what we'd suggest doing today.
A backup protects your data. It doesn't keep email running when Microsoft's own service is down.
What happened
The trouble started on Thursday 12 November. At 16:17 UK time Microsoft opened an incident (EX1550543) for people who couldn't reach their Outlook mailboxes, at first in the Americas. By 18:07 Microsoft said the problem could affect Microsoft 365 users in any region, and at 18:26 it opened a wider incident (MO1550821) covering the rest of Microsoft 365.
Downdetector logged more than 120,000 Outlook problem reports at the peak, from 74 countries and territories.
Overnight Microsoft paused all deployments and configuration changes, restarted servers, moved traffic around and added capacity. It reported partial recovery in some regions in the early hours of Friday, and said it was working to make that recovery hold. At the time of writing Microsoft hasn't given a time for a full fix.
The outage in numbers
16:17
Thursday, UK time, when Microsoft opened the Outlook mailbox incident
120,000
More than this many Outlook problem reports on Downdetector at the peak
74
Countries and territories reporting problems
What went wrong
Microsoft's early updates pointed to high load. As its engineers looked closer, they found there was no spike in traffic. Instead, a large number of servers dropped out after failing automated health checks, which pushed their work onto the servers that were left. Microsoft says a process on those servers that sets up secure connections became overwhelmed, and servers it brought back would fail again once traffic returned to them.
Microsoft has started rolling back a recent network configuration change that it says coincides with the start of the problem, but it hasn't confirmed that change as the cause. Microsoft has said a full root cause report will follow.
Importantly, this wasn't a cyber attack. Charles Lamanna, a Microsoft executive vice president, said: "There is no indication this is the result of malicious or cyber activity."
What's affected and what still works
The problem sits with Exchange Online, the service behind Outlook, so anything that needs your mailbox or calendar is affected. A lot of Microsoft 365 is carrying on as normal.
Where the outage is being felt
Affected
- Outlook mailboxes On the web, desktop and mobile, with incoming mail delayed
- Teams calendars Scheduling, invites and meeting changes
- Copilot Chat may not load or reach email, calendar and files
- Admin and security tools Parts of the admin centre, Intune, Purview and Safe Links in Defender for Office 365
Largely still working
- Teams chat Group chats and channel messages
- Teams calls and meetings Meetings already in the diary can still be joined
- SharePoint files Most file access, apart from features that rely on Exchange
Delayed email is normally queued by the sending server and retried, so most of it should arrive once mailboxes are back. It's still worth asking anyone waiting on something important to tell you by another route.
What we'd suggest doing today
Five things to do while Microsoft fixes it
- 1Check Service healthAdmin centre, incidents EX1550543 and MO1550821
- 2Leave your devices aloneNo reinstalling Outlook or resetting passwords
- 3Move internal chat to TeamsChats and calls are largely working
- 4Tell customers another wayWebsite, phone message or social media
- 5Watch for fake Microsoft emailsOutages are a favourite hook for phishing
- Check the official status. In the Microsoft 365 admin centre go to Health, then Service health, and look for EX1550543 and MO1550821. If the admin centre won't load, Microsoft posts updates at status.cloud.microsoft and on its Microsoft 365 Status account on X.
- Don't start fixing your own machines. This is a Microsoft problem, so reinstalling Outlook, rebuilding profiles or resetting passwords won't help, and it tends to leave a mess to tidy up afterwards.
- Use what's working. Teams chat and calls are largely fine, so use them for anything internal that would normally go by email.
- Let customers know. If people can't get an email through to you, a short note on your website or social media, or a message on your phone line, saves a lot of chasing.
- Be wary of anything claiming to fix it. Expect fake "verify your Microsoft account" emails and texts off the back of this. Microsoft won't ask you to sign in through a link to get your mailbox back.
What this teaches smaller businesses
Outages like this are rare, and they don't change our view: Microsoft 365 remains the right platform for most small businesses. Every cloud provider has an occasional bad day, and Microsoft 365 is still more dependable and better protected than the email servers small businesses used to run themselves.
What helps is a bit of planning that costs next to nothing:
- A one-page plan for when email is down: who checks the official status, how staff are told, and how customers can reach you.
- A contact list for staff, key customers and suppliers that doesn't live only in Outlook.
- Service health alerts in the admin centre going to someone who will act on them, ideally to an address outside Microsoft 365 as well.
- An honest look at backup. A Microsoft 365 backup is well worth having, because it protects you from deletion, ransomware and mistakes, but it doesn't keep email running during an outage like this one.
A backup protects your data. It doesn't keep email running when Microsoft's own service is down. Knowing that before the day it matters is the whole point.
If you'd like to check where you stand on backup, see our Microsoft 365 backup service.
How we can help
If you'd like to know how your business would cope with a day like yesterday, there are three easy ways to start:
- Run a free domain scan. It takes a minute and shows how your email security looks from the outside, including whether someone could send email pretending to be you.
- Book a free IT Health Check. A wider look at your setup, from Microsoft 365 and devices to backups, with an engineer on Teams or on your own.
at a time that suits you, and we'll talk through outage planning, backup or your Microsoft 365 setup without the jargon.
Want this handled for you? See Microsoft 365 support.
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IT Health Check
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