Microsoft Outlook outage: positive results from restarts, no all-clear

As of 9:29 p.m. ET on Nov. 12, Microsoft says restarting affected infrastructure in an isolated manner is giving "positive results," and it is applying capacity improvements for regions coming online (incident EX1550543). It has not said the outage is over, or when it will be.

Its Microsoft 365 Status account first posted at 12:54 p.m. ET that it was "investigating reports of users experiencing issues accessing Exchange Online mailboxes through multiple connection methods in the Americas."

What Microsoft said

At 1:07 p.m. ET the same account posted: "While we're working to mitigate impact, we've confirmed the issue may affect Microsoft 365 service connectivity for users in any region."

The first two posts point to the Microsoft 365 admin center, under EX1550543, for more detail. That page is for tenant admins, and we could not read it.

Later posts described a mitigation and a possible source. At 2:50 p.m. ET it posted: "We're testing a configuration change to address a problem that's causing servers to fail automated health checks and become unavailable. In parallel, we've initiated a restart of all affected servers and are monitoring health as they return to service."

At 3:19 p.m. ET it added that it has "not identified any recent change correlated with the start of impact." Its investigation indicates the failed health checks "may originate from a specific component that's responsible for processing server health," and it has "taken steps to prevent additional servers from being impacted."

At 4:00 p.m. ET it posted its first sign of recovery: "We've validated an alternative service health check method, which allowed a subset of affected servers to successfully return to service. We're now applying this change more broadly."

It added that it is "preparing automated recovery systems to continually detect and restart unresponsive servers, to maintain service stability while this change progresses." That was partial recovery.

At 4:40 p.m. ET it posted: "We're actively restarting and validating the affected servers to return them to service. In parallel, we're assessing whether reverting a small number of recent configuration updates we identified could help accelerate recovery." It points to EX1550543 and MO1550821 in the admin center. Microsoft does not say what MO1550821 covers.

That was an assessment, not a stated cause or a fix. The 3:19 p.m. statement that it had not identified a recent change is earlier history, and Microsoft has not explained how it fits with later posts.

At 5:09 p.m. ET it posted: "We're opening all available pathways to restore service, as our actions taken thus far have not provided the anticipated relief. We found a core process on affected servers is becoming overwhelmed, causing capacity loss."

It continued: "To validate a potential recovery, we're isolating a portion of infrastructure, restarting affected components, and reintroducing traffic to confirm the services remain stable before applying the change more broadly."

That is a test of a possible recovery, not a fix. Microsoft does not say the configuration updates it mentioned at 4:40 p.m. caused the problem, and it does not link them to this post.

At 6:04 p.m. ET it posted: "We're returning a portion of affected servers to the service, and they remain stable so far. We're also shifting traffic to alternate routes wherever possible and observing limited recovery."

It added: "In parallel, we've streamlined the process of returning the remaining affected servers to service. As capacity is restored, users may experience a gradual recovery as their clients reconnect."

That was partial, limited recovery. Microsoft did not say how many servers were back or when the rest would be.

At 7:06 p.m. ET it posted a setback: "The servers we returned to service can become unresponsive again once they receive traffic; we're analyzing diagnostic data to determine what's triggering the behavior."

It added: "In parallel, we're temporarily limiting which types of traffic can reach the affected infrastructure in some locations. Additionally, we're rebuilding a subset of affected servers using a previous configuration to validate if this prevents them from becoming unresponsive."

The rebuild is a test of whether it stops the servers failing. Microsoft does not say what caused the problem, and it does not link that previous configuration to the configuration updates it mentioned at 4:40 p.m. It has not announced a fix.

At 8:01 p.m. ET it posted that it had "reviewed known impact scenarios and revised the list of impacted services and features." The list is in the "more info" section of MO1550821 in the admin center or at status.cloud.microsoft. It added that it is "continuing our work to isolate the issue affecting server availability."

We could not read the revised list, so we cannot say which services it names.

At 8:59 p.m. ET it posted: "We're seeing positive results with our efforts to restart affected infrastructure and recover server availability in an isolated manner."

It continued: "We're actively monitoring the performance of these portions of infrastructure to verify stability, which we suspect will support improved availability as these actions are subsequently expanded more broadly."

Those are results for isolated portions of infrastructure. Microsoft does not say how many servers are back, and the 7:06 p.m. warning that returned servers can fail again is the last problem it described.

At 9:29 p.m. ET it posted: "We're applying infrastructure capacity improvement where possible to help support traffic in regions coming online."

It added: "We're continuing to monitor the results of changes applied so we can identify strategic actions that can help to improve service health across all affected regions." Microsoft did not give a time for recovery.

What Downdetector shows

Downdetector's US Outlook page showed reports climbing from about 1,240 at 12:29 p.m. ET to a peak of 130,877 at 1:14 p.m. ET. The latest point we saw, 1:44 p.m. ET, was 98,308. We have no newer reading.

Downdetector counts reports submitted by users. These are not Microsoft data and not confirmed outages. The chart as we read it at 2:00 p.m. ET:

• 12:29 p.m.: 1,240
• 12:44 p.m.: 23,943
• 12:59 p.m.: 99,453
• 1:14 p.m.: 130,877 (peak)
• 1:29 p.m.: 117,271
• 1:44 p.m.: 98,308

9to5Mac, writing at 1:54 p.m. ET, reported a widespread Outlook outage that it said began about an hour earlier. It cited more than 100,000 Downdetector reports and said the page it usually checks for Outlook status "appears to maybe be down as well." It did not quote Microsoft.

What you can do

• If you are a Microsoft 365 admin, check the admin center for incidents EX1550543 and MO1550821. Microsoft also points to status.cloud.microsoft if the admin center is not available to you.
• Otherwise, wait for Microsoft's updates. As of 9:29 p.m. ET, Microsoft is still monitoring results and has not said service is restored, so expect it to be uneven. We have no fix to offer, and Microsoft has not published a workaround.

What isn't announced

• The confirmed root cause. At 3:19 p.m. Microsoft said the failed health checks may come from one component and that it had not identified a recent change tied to the start. At 4:40 p.m. it said it is assessing a revert of a small number of recent configuration updates. At 5:09 p.m. it said a core process on affected servers is overwhelmed. At 6:04 p.m. it reported limited recovery, and at 7:06 p.m. said returned servers can become unresponsive again while it analyzes the trigger. At 8:59 and 9:29 p.m. it described positive results and capacity work, not a cause. It has not said what started the problem or whether those updates caused it.
• When it will be fixed, or when all affected servers will be back. Microsoft has not said how many servers are back.
• Who is affected. Microsoft named Exchange Online mailboxes, first in the Americas, then said connectivity for Microsoft 365 users in any region may be affected. Its status page, when we re-read it at about 9:35 p.m. ET, still said users "may be unable to connect to multiple Microsoft 365 services" without naming them. Posts on social media say Teams, SharePoint, Copilot and Defender are also hit; we found no Microsoft statement confirming that.
• Whether the outage has ended. Microsoft's last post we read, at 9:29 p.m. ET, says it is applying capacity improvements and monitoring results; it is not an all-clear.

What we checked

We read Microsoft's @MSFT365Status posts, including the 2:50 to 9:29 p.m. ET ones, on X on Nov. 12. We read the 7:06 p.m. post in full at 7:08 p.m. ET, and the last three in full at 9:35 p.m. ET. We read Downdetector's US Outlook page at 2:00 p.m. ET and did not refresh its figures.

Microsoft's public status page, status.cloud.microsoft, showed a "Service degradation" notice, "Users may be unable to connect to multiple Microsoft 365 services", at 4:24, 4:54, 5:24 and 7:08 p.m. ET, and when we re-read it at about 9:35 p.m. ET, with no further detail.

We could not open the admin center. We did not test any mailbox.

This story will be updated when Microsoft posts an all-clear or a new EX1550543 update. Related: an Outlook flaw being exploited, with an Office update, and the iCloud outage on Nov. 10.