What the Microsoft 365 Outage Taught Us About Email

If your inbox has been quiet since Thursday afternoon, you’re not alone. A global Microsoft 365 outage has left businesses, courts and government departments around the world unable to reliably send or receive email. At the peak, nearly 140,000 people had reported Outlook problems on Downdetector, which the BBC says is more than 2,000 times the normal level.

Here at Bronco, we’re in the fortunate position of not running our email on Outlook 365. Our inboxes have kept working, and so have our clients’ emails, as long as they aren’t on Microsoft’s platform. We handle around over 100,000 emails every day, and it’s moments like this that show just how much people and businesses rely on email to function.

What’s happened so far

The trouble started on Thursday 12 November. Microsoft says its Microsoft 365 incident began at 1:26pm ET (6:26pm UK time), although it had already been looking into Exchange Online mailbox problems in the Americas earlier that day.

It isn’t just Outlook. Microsoft’s own advisory lists Exchange Online, Teams, SharePoint Online, Microsoft 365 Copilot and Defender XDR as potentially affected. Downdetector data suggests users and critical infrastructure in 74 countries and territories have been hit.

The list of organisations caught up in it is long:

• Government agencies in Australia, Japan and the US, including the US House of Representatives
• Courts in Singapore and the Philippines, which asked people to phone about urgent matters
• Airlines IndiGo and Akasa Air, whose email support went down
• AI companies OpenAI and Anthropic, which had problems with their Microsoft connectors

One US electric truck maker, Workhorse Group, even moved its quarterly results announcement back four days because of the disruptionThat’s what happens when email stops.

How much email runs through Microsoft?

Microsoft doesn’t publish a single daily total for Outlook and Exchange Online. But the numbers it does share give a sense of scale.

• 5.2 billion emails a day: that’s how many emails Microsoft screens on average for malware and phishing, according to its Digital Defense Report 2026.
• 450 million+ paid business seats: Microsoft said in January 2026 that paid commercial Microsoft 365 seats were over 450 million, and most of those plans include Exchange Online and Outlook (HCA Magazine). Analysts estimate the figure is now approaching 470 million.
• 117 emails a day: the number the average worker receives, according to Microsoft’s own Work Trend Index research.

Across the world, an estimated 392.5 billion emails are sent and received every day in 2026, by around 4.73 billion users. That works out at roughly 4.5 million emails every second.

Put simply, hundreds of millions of working people rely on Microsoft for email, and each of them is dealing with more than a hundred messages a day. When that pipeline stalls, quotes don’t get sent, invoices don’t land and enquiries go unanswered.

What’s causing it?

Microsoft’s first explanation was “elevated load” on its infrastructure. A large number of servers became “unexpectedly unavailable”, which pushed extra traffic onto the remaining servers and put them under strain (BBC). Microsoft later said servers were failing automated health checks, effectively taking themselves out of service.

Digging further, Microsoft identified a process responsible for establishing secure connections on the affected servers as a key factor. It’s also reversing a recent network configuration change that coincided with the start of the outage, to see whether that contributed. As a precaution, it has paused all deployments and configuration changes.

Our reading is that this looks like a change gone wrong, followed by a cascade. As servers dropped out, the rest got overloaded, and servers that were restarted risked falling over again as soon as traffic returned. Australia’s Cyber Security Minister Tony Burke made a similar point, saying it appeared “in some ways similar to what we saw with respect to CrowdStrike where there is an update that has gone awry” (Reuters).

Importantly, Microsoft executive Charles Lamanna has confirmed the outage was not caused by a cyber security breach (Business Standard).

Can Microsoft fix it?

Yes, but it’s taking longer than anyone would like. Overnight, Microsoft admitted its fixes were “not taking as expected” and that it was looking at alternative ways to increase capacity. By 7:59am GMT on Friday, it reported “positive results” on stability and capacity and was rolling those actions out across affected regions (BBC).

So recovery is likely to be gradual rather than a single “back on” moment. Microsoft has warned users may see a gradual recovery as their apps reconnect, and it has promised a full root cause in a post-incident report once things are stable.

If you’re affected, Microsoft’s advice is not to delete and re-add your account while the incident is live, because it won’t fix a server-side problem and could complicate recovery.

A bigger picture of fragile tech

This isn’t a one-off. Reuters notes it is the second disruption to Microsoft 365 services this year, following one in January. Across the big cloud providers, one tracker counts 18 major outages in 2026 up to late October, already more than the 16 in the whole of 2025.

At the same time, cyber attacks keep climbing. The National Cyber Security Centre received 1,831 reports of cyber attacks in the year to August 2026, up from 1,727 the year before, and warned that AI is accelerating the scale and speed of the threat. Check Point found organisations faced an average of 2,550 attacks a week in October, up 32% year on year, with Europe seeing the fastest growth at 39% (Check Point).

Closer to home, 43% of UK businesses, around 612,000, reported a breach or attack in the last 12 months, and phishing was the most common type (GOV.UK). Yet only 25% have a formal incident response plan.

Outages like this are also a gift to scammers. Expect fake “restore your Outlook access” emails and texts over the coming days, so be wary of any message asking you to log in or reset a password.

What businesses should take from this

As cyber security adviser Jake Moore put it, the outage hammers home the need for contingency plans for communication during incidents (BBC). A few practical steps:

1. Know your backup channel. Phone, text, WhatsApp or a website contact form can keep enquiries coming in when email stops.
2. Don’t put all your eggs in one basket. If your email, files and calls all sit with one provider, one fault takes them all down.
3. Keep your website working for you. Make sure your contact details, phone number and forms are visible, so customers can still reach you.
4. Write a simple incident plan. Who tells clients, how, and what you say.
5. Train your team on phishing. Especially in the days after a big outage.

We were lucky this time. But email is the backbone of how most businesses win and keep customers, and this week has been a reminder that it’s worth knowing what you’d do without it.

If you’d like help reviewing how your website and digital channels would hold up during an outage, get in touch with the Bronco team.

Figures correct at the time of writing, Friday 13 November 2026, morning UK time. The outage is ongoing and details may change.