Microsoft 365 Outage Live Updates: Microsoft Says Outlook and Exchange Online Restored
Live updates on the Microsoft 365 and Exchange Online outage that has deferred mail to Outlook.com, Hotmail and Office 365 since 12 November, with every official Microsoft update and what senders should do now.
Mail sent to Microsoft mailboxes piled up in sender queues from Thursday 12 November 2026. Microsoft's mail servers began answering a large share of delivery attempts to Outlook.com, Hotmail, Live, MSN and Office 365 with temporary errors at about 17:30 UTC, according to SparkPost's status page. Microsoft declared the consumer incident (Outlook.com, Hotmail) remediated at 03:51 UTC on 14 November, and at 05:42 UTC it cleared the Microsoft 365 business incident from its public status page, which now shows service as available. The live timeline below follows every official update. Microsoft tracked the problem as EX1550543 for Exchange Online, alongside a wider Microsoft 365 incident, MO1550821, that also touched Teams, SharePoint Online and Copilot.
For senders, this is not a reputation problem and not a block. It is a capacity failure on the receiving side, and nearly every major sending platform reported the same symptom at the same time: deferrals, delivery delay events and growing queues for Microsoft-hosted recipients. The risk now is what happens to messages whose retry window runs out before Microsoft recovers.
✓ Sender update: Microsoft declared the incident resolved
You can resume normal sending to Outlook, Hotmail and Microsoft 365 addresses
Microsoft declared the consumer incident remediated at 03:51 UTC on 14 November and cleared the Microsoft 365 business incident from its status page at 05:42 UTC. Our recommendation now:
Newsletters and campaigns: resume sends to Microsoft-hosted recipients gradually instead of releasing every rescheduled campaign at once, and watch deferral rates for a few hours.
Cold outreach: restart sequences to Microsoft-hosted prospects gradually and watch deferrals and bounces for a few hours before returning to full volume.
Transactional and one-to-one mail: send as normal. Retry messages that bounced or expired during the outage where they still matter, such as Mailgun messages that expired with code 602 ("Too old"), but do not resend mail that was accepted, since it should have been delivered.
How to find these recipients: consumer addresses at outlook.com, hotmail.*, live.* and msn.com, plus business domains whose MX record ends in mail.protection.outlook.com (Microsoft 365). If Microsoft deferrals continue on your side, check your own setup and the live timeline.
Key facts
- Who: Microsoft, consumer mail (Outlook.com, Hotmail, Live, MSN) and Microsoft 365 business mail (Exchange Online)
- Start: 12 November 2026, about 17:30 UTC
- Incident IDs: EX1550543 (Exchange Online) and MO1550821 (Microsoft 365)
- Symptom for senders: temporary 4xx deferrals on a large share of delivery attempts
- Platforms reporting impact: SparkPost, Resend, Mailgun, beehiiv, SMTP2GO and others
- Status: resolved. Microsoft declared consumer services (Outlook.com, Hotmail) remediated at 03:51 UTC on 14 November and cleared the Microsoft 365 business incident from its status page at 05:42 UTC on 14 November, now showing service as available
- Delayed mail: Microsoft extended its email timeout to 48 hours to preserve messages during recovery
- Cyberattack: Microsoft says it has no evidence of malicious activity and will publish a post-incident report
Live timeline
✓ Resolved: final update 05:42 UTC, 14 November
Resolved. Microsoft declared the consumer incident for Outlook.com and Hotmail remediated at 03:51 UTC on 14 November, saying services had fully recovered and the backlog of email messages had been processed. At 05:42 UTC it cleared the Microsoft 365 business incident (Exchange Online) from its public status page, which now shows service as available. SparkPost, Mailgun and beehiiv report delivery to Microsoft back to normal. Messages that expired during the outage, such as Mailgun's code 602 ("Too old"), were not delivered and need to be retried. Microsoft has promised a post-incident report with the root cause.
All times UTC, newest first. Green tags are Microsoft's own updates (Microsoft 365 Status account and service health page); grey tags are sending platforms' status pages.
14 Nov, 05:42Microsoft service health
Microsoft clears the Microsoft 365 business incident and its status page now shows service as available, ending the outage. At 05:42 UTC Microsoft replaced the Exchange Online incident notice on its public Microsoft 365 status page with its standard message and set the status to available, after declaring the consumer Outlook.com and Hotmail incident remediated at 03:51 UTC. Microsoft has said it will publish a post-incident report with the root cause. Source
14 Nov, 03:51Microsoft service health
Microsoft declares the consumer Outlook.com and Hotmail incident remediated, while Microsoft 365 business mail is still not resolved. In its final consumer update at 03:51 UTC, Microsoft says services across the previously affected environments have fully recovered and the backlog of email messages has been processed, and it now lists Microsoft 365 (Consumer) as service restored and Outlook.com as operational. It gives a start time of 10:05 UTC on 12 November and an end time of 16:10 UTC on 13 November for the consumer event. The Microsoft 365 business incident is still shown as a service degradation, with its last update at 22:00 UTC on 13 November. Source
14 Nov, 03:18Microsoft service health
Microsoft says recovery is still holding, but the incident is not yet remediated. In its 03:18 UTC consumer update it reports continued sustained recovery of impacted services, keeps monitoring service health metrics to confirm no further action is needed to fully remediate the issue, and is still checking that the backlog of email is fully processed before it considers the issue remediated. Microsoft 365 (Consumer) is still listed as a service degradation, and the next consumer update is due by 04:00 UTC on 14 November. Source
14 Nov, 01:51Microsoft service health
Microsoft says recovery is still sustained but the incident is not yet remediated. In its latest consumer update it reports continued recovery of impacted services, keeps monitoring service health metrics to confirm no further action is needed, and is checking that the email backlog is fully processed before it considers the issue remediated. Microsoft 365 (Consumer) is still listed as a service degradation, and the next consumer update is due by 04:00 UTC on 14 November. Source
14 Nov, 00:39Microsoft service health
Microsoft says recovery is holding for consumer services but the incident is not yet remediated. On its consumer status page it reports sustained recovery across the previously affected environments, keeps monitoring service health for an extended period, and is checking that the email backlog built up during the outage is fully processed before it considers the issue remediated. Microsoft 365 (Consumer) is still listed as a service degradation, while Outlook.com shows as operational; the next consumer update is due by 02:00 UTC and the next business update by 02:30 UTC on 14 November. Source
13 Nov, 22:00Microsoft service health
Microsoft says service recovery is sustained across the previously affected environments, but it is monitoring for an extended period before calling the incident resolved. It is also tracking the backlog of email built up during the outage and will only consider the issue resolved once all those messages process successfully, adding that most impact scenarios for related Microsoft 365 products have been addressed. The incident stays listed as a service degradation, with the next business update due by 02:30 UTC on 14 November. Source
13 Nov, 20:02Microsoft service health
Microsoft says it is still draining queued messages and has no ETA yet for full recovery. As its infrastructure stabilizes, it is rebalancing traffic, and it warns that sign-in and access may recover before mail flow fully returns to normal, so email delivery can keep lagging. The incident stays listed as a service degradation for Microsoft 365 business and consumer services, with the next update due by 00:00 UTC on 14 November. Source
13 Nov, 18:50Mailgun
Mailgun says delivery to Microsoft mailbox providers is back to normal, but some messages were not delivered. Messages that expired with status code 602 and the message "Too old" were never delivered and need to be retried by the sender. Source
13 Nov, 18:57Microsoft service health
Microsoft's consumer status page still lists the incident as a service degradation, even though it shows Outlook.com as operational. Microsoft repeats that it sees broad recovery and stability and has addressed the underlying issue, while it keeps restoring service to remaining customers and regions. It has not declared the incident resolved, and the next consumer update is due by 21:00 UTC. Source
13 Nov, 17:57Microsoft service health
Microsoft says it has addressed the underlying issue and sees broad recovery and stability across its services, while it keeps restoring service to remaining customers and regions. It says the incident was introduced by an issue during an earlier network capacity upgrade that surfaced after a recent network change, and was not related to cyber or AI agents. The incident stays listed as a service degradation, with a full post-incident report promised and the next update due by 20:00 UTC. Source
13 Nov, 17:09beehiiv
Sending platform beehiiv closes its own Microsoft delivery incident, but Microsoft has not yet declared the outage resolved. Before closing it, beehiiv reported increased deliveries and fewer deferrals to Microsoft inboxes as it worked through its backlog of queued mail. Source
13 Nov, 16:24Microsoft service health
Microsoft says it sees signs of sustained recovery across affected consumer services such as Outlook.com, while its root cause investigation continues. It is monitoring Outlook.com, OneDrive, OneNote, Microsoft To Do, Teams and Microsoft 365 for the web to confirm service health stays stable. The consumer incident stays listed as a service degradation, with the next update due by 18:30 UTC. Source
13 Nov, 16:20SparkPost
SparkPost says delivery to Microsoft mailboxes is back to normal on its platform and closes its own incident. It says Microsoft's errors dropped sharply from about 13:30 UTC, delivery returned to normal rates by 14:35 UTC and the rest of its retry queue will finish over the next few hours. Messages with a short expiration setting may have expired and bounced, so time-sensitive mail may need resending. Source
13 Nov, 16:07Microsoft service health
Microsoft says it remains focused on residual impact and on making service restoration reliable for Microsoft 365 business users. It is still assessing recovery across connection methods such as Outlook on the web, Outlook desktop and Exchange ActiveSync, and warns that email delivery may still be delayed. The incident stays listed as a service degradation, with the next update due by 18:00 UTC. Source
13 Nov, 14:56Microsoft service health
Microsoft reports sustained improvements in service availability as recovery progresses across affected Microsoft 365 services, but some users may still see intermittent connectivity issues or delayed email delivery. It is validating recovery across connection methods and monitoring stability. The incident stays listed as a service degradation, with the next update due by 16:00 UTC. Source
13 Nov, 14:48Microsoft service health
The public status page still lists Microsoft 365 as a service degradation. In the consumer list, Outlook.com is now marked operational, while the Microsoft 365 consumer entry stays degraded. Microsoft says it has no evidence of malicious activity and will publish a full post-incident report with the root cause once mitigation is complete. Source
13 Nov, 14:17Microsoft
Email queues are significantly reduced and approaching normal levels. Some users may still see intermittent access issues or delayed email delivery while Microsoft restores the remaining infrastructure and investigates residual issues. View post
13 Nov, 13:32Microsoft
Recovery continues: broader improvements in North America, sustained improvements across much of Europe and encouraging signals in Asia Pacific. The focus is on stabilising recovered infrastructure and reducing delayed email queues. View post
13 Nov, 12:09Microsoft
Service availability and email delivery are improving across a growing portion of the affected infrastructure. The extended 48-hour email timeout stays in place while delivery catches up. View post
13 Nov, 11:11Microsoft
Recovery actions are completed on portions of the infrastructure and traffic is gradually restored, with improvements in mailbox access and delayed email processing. View post
13 Nov, 10:28Microsoft
Recovery progresses in phases, but capacity is not yet back to baseline. Microsoft confirms the email timeout window is extended to 48 hours while queues and backlogs are processed. View post
13 Nov, 09:24Microsoft
Early stabilisation and capacity improvements. To preserve delayed mail, Microsoft extends the email timeout to 48 hours. View post
13 Nov, 07:44Microsoft
Positive results for stability and capacity after the latest traffic optimisation; Microsoft applies these actions more broadly across affected regions. View post
13 Nov, 05:01Microsoft
Multiple workstreams are running to reduce impact, clear the current blocker and return portions of the infrastructure to a healthy state. View post
13 Nov, 04:36Microsoft
Partial recovery in regions where traffic adjustments were applied (traffic protocols, redistribution, targeted traffic blocking), but the recovery is not sustained. View post
13 Nov, 03:19SparkPost
About two thirds of SparkPost's delivery attempts to Microsoft are still deferred. Relaying Microsoft, it says the changes applied are not working as expected and that there is no recovery estimate. Source
13 Nov, 03:10SparkPost
The rate of temporary errors from Microsoft fell by about half over the previous hour; more queued mail is delivered on retry. Source
13 Nov, 01:11SparkPost
Relaying Microsoft: a process that establishes secure connections is overwhelmed, and Microsoft is rolling back a recent network configuration change that coincided with the start of the problem. Source
13 Nov, 00:06Microsoft
Servers returned to service can become unresponsive again once they receive traffic. Microsoft limits which types of traffic reach the affected infrastructure in some locations and rebuilds a subset of servers with a previous configuration. View post
12 Nov, 23:54SparkPost
After more than six hours, messages with expirations of several hours start to expire and turn into bounce events. Source
12 Nov, 23:04Microsoft
A portion of affected servers is back in service and stable so far; traffic is shifted to alternate routes and limited recovery is observed. View post
12 Nov, 22:38Mailgun
Delivery to Microsoft mailbox providers is deferred, with no mail loss at this time. Source
12 Nov, 22:09Microsoft
Actions taken so far have not provided the anticipated relief. A core process on affected servers is overwhelmed, causing capacity loss; Microsoft isolates part of the infrastructure to test a recovery. View post
12 Nov, 21:51beehiiv
Much higher deferral rates to Outlook, Office 365 and other Microsoft-hosted inboxes. No mail lost. Source
12 Nov, 21:40Microsoft
Affected servers are being restarted and validated; Microsoft assesses whether reverting a small number of recent configuration updates could speed up recovery. View post
12 Nov, 21:30SMTP2GO
The Outlook outage is hitting delivery for many customers; SMTP2GO is also investigating delays to Gmail recipients. Source
12 Nov, 21:00Microsoft
An alternative health check method returns a subset of servers to service; Microsoft applies it more broadly and prepares automated recovery to restart unresponsive servers. View post
12 Nov, 20:19Microsoft
No recent change found that correlates with the start of impact; the failed health checks may come from a component that processes server health. View post
12 Nov, 20:01SparkPost
Delivery attempts to Outlook.com, Hotmail, Live, MSN and Office 365 get temporary errors such as 451 4.7.0 Temporary server error. Senders are told not to resend. Source
12 Nov, 19:50Microsoft
Microsoft tests a configuration change for servers failing automated health checks and restarts all affected servers. View post
12 Nov, 19:31Microsoft
The elevated load is not caused by more traffic but by a number of servers being unexpectedly unavailable. View post
12 Nov, 19:12Microsoft
All deployments paused; traffic moved off the affected infrastructure and servers restarted. View post
12 Nov, 18:48Microsoft
Connection traffic is redistributed across Microsoft's worldwide infrastructure to balance the load. View post
12 Nov, 18:35Microsoft
Part of the infrastructure is under elevated load across multiple regions. Incident MO1550821 is opened alongside EX1550543. View post
12 Nov, 18:07Microsoft
The issue may affect Microsoft 365 connectivity for users in any region. View post
12 Nov, 17:54Microsoft
Microsoft investigates Exchange Online mailbox access issues in the Americas under EX1550543. View post
12 Nov, about 17:30Start
Microsoft's mail servers start answering a large share of delivery attempts with temporary errors (time reported by SparkPost). Source
What happened
The disruption started on the afternoon of 12 November in Europe and mid-morning in the Americas. Users lost access to webmail and inbound mail slowed down, while sending servers began receiving temporary rejections instead of acceptances. The deferral responses reported by senders include 451 4.7.0 Temporary server error, 421 4.3.2 The maximum number of concurrent server connections has exceeded a limit and 451 4.7.700 PFA agent busy.
Microsoft's explanation evolved through the evening. It first said a large number of servers had become unavailable and were failing automated health checks, leaving the remaining systems to carry the load, although overall traffic had not increased. It then said a fix tested on a group of affected servers would be rolled out more widely, before reporting that the recovery steps had not brought the expected relief. Later updates, relayed by SparkPost, said a process that sets up secure connections had been overwhelmed and that Microsoft had started rolling back a recent network configuration change that coincided with the start of the problem.
The situation overnight
By the last SparkPost update, about ten hours into the incident, Microsoft said the changes it had applied were not working as expected and that it was pursuing other ways to add capacity. Around two thirds of SparkPost's delivery attempts to Microsoft were still being deferred, and Microsoft gave no time for full recovery. Resend's status page, still in monitoring at its latest update, likewise noted that Microsoft had provided no recovery estimate.
Recovery on 13 November
Microsoft's own updates turned positive in the morning of 13 November. At 09:24 UTC it reported early stabilisation and said it had extended the email timeout to 48 hours to preserve delayed mail. By 14:17 UTC it said email queues were significantly reduced and approaching normal levels, with some users still seeing intermittent access issues or delayed delivery. Microsoft says it has found no evidence of malicious activity and will share a full post-incident report with the root cause once mitigation is complete.
How sending platforms are handling it
The provider notices agree on the basics. SparkPost says its own systems are working normally and it is queuing affected messages. Mailgun says messages are deferred and there is no mail loss at this time. beehiiv reports much higher deferral rates and says no mail has been lost, but delivery to Microsoft-hosted inboxes may be delayed. Resend says the incident is not its own and that it keeps retrying delayed deliveries automatically. SMTP2GO also reported delivery delays to Gmail recipients while it investigated.
The common warning is about expiry. SparkPost cautioned that messages with short expiration settings could expire first, then messages with expirations of several hours as the outage dragged on, and that expired messages generate bounce events and leave the queue. Resend said emails may bounce if the outage outlasts its retry window, and that those can be retried once Microsoft recovers. Both platforms asked customers not to resend queued messages manually, since that only creates duplicates.
What it means for senders
What changes
Email to Outlook.com, Hotmail and Microsoft 365 mailboxes is being deferred on a large scale because of a Microsoft outage, so messages are delayed and some may bounce when their retry window expires. The deferrals are on Microsoft's side and say nothing about your sender reputation.
Who is affected
Any sender with Microsoft-hosted recipients, whatever platform they use: B2C lists heavy in Outlook.com and Hotmail addresses, and B2B senders whose customers run Microsoft 365. Time-sensitive mail such as one-time codes and password resets is hit hardest.
When
Since about 17:30 UTC on 12 November 2026, recovering from 13 November. Microsoft declared the consumer incident (Outlook.com, Hotmail) remediated at 03:51 UTC on 14 November and cleared the Microsoft 365 business incident at 05:42 UTC on 14 November, about 36 hours after the first errors.
Action checklist
- Do not resend queued mail while it is still deferred: your platform is retrying it, and a manual resend creates duplicates once Microsoft recovers.
- Treat these bounces as temporary: do not suppress Outlook.com, Hotmail or Microsoft 365 addresses that bounced because their retry window expired during the outage.
- Pause or reschedule non-urgent campaigns to Microsoft-heavy segments until deferral rates fall back to normal.
- Offer a fallback for codes and resets, such as a resend button with a fresh code or another channel, rather than replaying stale one-time codes in bulk.
- Check your retry and expiry settings: if you run your own MTA, make sure the queue lifetime is long enough to ride out a long incident.
- Exclude the outage window from deliverability reporting, since open, click and delivery rates to Microsoft will be distorted.
- Remember the 48-hour window: Microsoft extended its email timeout to 48 hours, so mail it has accepted but not yet delivered should still arrive; check before treating it as lost.
- Retry bounced messages after recovery where they still matter, and follow EX1550543 on the Microsoft 365 status page.
Not a reputation issue
Mass 4xx responses from one mailbox provider can look alarming in a dashboard, but the pattern here is clear: the same deferrals hit every platform at once, regardless of sender. That separates this incident from filtering decisions such as Outlook.com's recent move to bounce mail from domains without DMARC, which do depend on how you send. If your Microsoft deferrals continue after Microsoft declares recovery, that is the moment to look at your own setup, starting with our guide to hard and soft bounces.
Sources
- Microsoft 365 Service Status (primary source), incidents EX1550543 and MO1550821
- Microsoft 365 Status on X: EX1550543 update thread (primary source), 12 and 13 November 2026
- SparkPost Status: Microsoft outage, delays delivering to Outlook, Hotmail and Office 365, updates of 12 and 13 November 2026
- Resend Status: Microsoft 365 Incident
- Mailgun Status: Delivery Delays for Microsoft Mailbox Providers
- beehiiv Status: Emails to Outlook and Office365 inboxes are experiencing delays
- SMTP2GO Status: Delivery Delays, Outlook and Gmail
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