A widespread Microsoft 365 service outage is affecting organisations in the UK and around the world. Some users are unable to access email in Outlook, connect to Exchange Online or use Microsoft 365 features that depend on email and calendar services.
Microsoft is tracking the incident under EX1550543 for Exchange Online and MO1550821 for the wider Microsoft 365 impact. The exact experience varies by organisation, region and service, so one employee may be working normally while another sees connection errors, delayed email or incomplete functionality.
Latest verified update: At 20:02 GMT, Microsoft said infrastructure was stabilising and customers may see improved sign-in and access. Engineers are still draining queued messages and rebalancing traffic, so email delivery and other processing may continue to catch up after access returns. Microsoft has not provided an estimated time for full recovery.
Is Microsoft 365 down today?
Microsoft 365 access is improving for many users as infrastructure stabilises. However, Microsoft is still draining queued messages and rebalancing traffic, so email delivery and other processing may remain delayed even after sign-in and mailbox access return.
The clearest description is still a Microsoft 365 service incident in recovery. Microsoft has not marked the incident resolved and has not provided an estimated time for full recovery.
What Microsoft has said happened
Microsoft says the incident was introduced by an issue during an earlier network capacity upgrade which surfaced following a more recent network change. The resulting infrastructure and traffic-management problems caused servers to become unavailable or unresponsive, reducing capacity and affecting Exchange Online and connected Microsoft 365 services.
Recovery required Microsoft to isolate affected infrastructure, restart and remediate servers, adjust traffic handling and return services in controlled stages. Microsoft says it restored services gradually because of the scale of demand, validating stability at each stage before expanding recovery.
Microsoft now says the underlying issue has been addressed. Engineers are continuing to restore service for the remaining customers and regions and will publish a full post-incident report after their review is complete.
Microsoft says this was a technical issue and was not related to a cyber incident or AI agents.
Which Microsoft 365 services may be affected?
Exchange Online and Outlook are at the centre of the incident. Microsoft has also listed possible impact to features across other services where they interact with Exchange Online or email.
- Outlook and Exchange Online: mailbox access, sending and receiving email, calendar access or delayed delivery.
- Microsoft Teams: core calls, meetings, group chats and channel messages remain available, but calendars, scheduling, meeting edits and other Exchange-dependent features may fail.
- SharePoint Online: some external sharing and Exchange-dependent features may be affected. Microsoft says direct access to files stored in SharePoint remains functional.
- Microsoft 365 Copilot: Copilot Chat or features that need access to work email, calendars and files may fail.
- Microsoft Defender and Purview: policy evaluation and governance actions that rely on Purview Data Loss Prevention or Information Protection signals may be delayed or fail. Microsoft has also reported possible delays or failures in some non-human identity features and Defender portal pages.
- Intune, Planner, To Do, Power BI and Microsoft 365 administration: particular features including device enrolment, device check-in, task operations and some administrative pages may be affected.
- Other connected services: Microsoft has also reported impact to Microsoft 365 Apps Admin Center, Microsoft Fabric, Windows 365 and Universal Print in specific scenarios.
This does not mean every part of every listed service is unavailable. Microsoft has said that functions which do not depend on Exchange Online may continue to work normally.
What should your business do during the outage?
1. Do not make unnecessary account changes
If several people are affected at the same time, repeated password resets, profile rebuilds or application reinstalls are unlikely to help and can create extra work once the service recovers. Only make a local change where there is separate evidence of a device or account problem.
2. Avoid repeatedly sending the same email
Email may be delayed rather than lost. Microsoft has extended the email timeout window to 48 hours to help protect delayed messages while queues are processed. Repeated resends can create duplicate messages when normal delivery resumes. For something genuinely time-sensitive, use a telephone call or another agreed communication route.
3. Save work and expect intermittent recovery
Service recovery may not happen at the same time for every user. Save local work, check that important changes have synchronised and allow time for Outlook, Teams and other Microsoft 365 clients to reconnect.
4. Check official service health information
Microsoft 365 administrators should follow incidents EX1550543 and MO1550821 in the Microsoft 365 admin centre. If the admin centre is unavailable, use the public Microsoft service health page.
5. Keep an alternative contact route available
Businesses that rely on email for customer enquiries, approvals or urgent operational messages should make a telephone number or another approved route visible until Microsoft confirms recovery.
Can an IT provider fix a Microsoft 365 outage?
An IT provider cannot repair Microsoft’s cloud infrastructure. What we can do is confirm whether the symptoms match the wider incident, rule out an unrelated local problem, explain which services are affected and help you use sensible alternatives while Microsoft restores capacity.
For managed clients, baseMSP is monitoring Microsoft’s communications and will distinguish this outage from tenant, account, device or network issues that still need separate investigation.
Does Microsoft 365 backup keep email online?
No. Independent Microsoft 365 backup protects recoverable copies of business data; it does not keep Outlook or Teams online during a Microsoft service outage. Backup and service availability solve different problems, and a resilient plan should recognise that distinction.
What happens next?
Microsoft is continuing to drain queued messages, rebalance traffic and monitor stability. Service access may recover before email delivery and connected processing fully normalise. Microsoft has not provided an estimated time for full recovery and has promised a full post-incident report once its review is complete. We will publish a final update when Microsoft formally confirms that the incident is resolved.
If your business is affected and you need help separating the Microsoft outage from a local issue, call baseMSP on 01252 268552. During a Microsoft email incident, calling is the safest route for anything urgent.
Frequently asked questions
Is Outlook down in the UK?
Microsoft has confirmed a multi-region service degradation that may affect users in the UK. Sign-in and mailbox access are improving for many users, but email delivery and other processing may remain delayed while Microsoft drains queues and rebalances traffic.
Is Microsoft Teams down?
Some Microsoft Teams features are affected, particularly those that depend on Exchange Online, email or calendar services. Microsoft says core calls, meetings, group chats and channel messages remain available.
Was the Microsoft 365 outage caused by a cyber attack?
No evidence currently indicates a cyber attack. Microsoft says this was a technical issue associated with an earlier network capacity upgrade and a subsequent network change, and was not related to cyber activity or AI agents.
Should I reset my Microsoft 365 password?
Not simply because Outlook or Teams is unavailable during this incident. If multiple users are affected, wait for service recovery unless there is separate evidence that your password or account is the problem.
Where can I see the official Microsoft 365 status?
Microsoft 365 administrators can check Service health in the admin centre using incident references EX1550543 and MO1550821. Microsoft also publishes a public service health page.
