The confirmed problem is with the management portal. Nothing so far shows that mail itself has stopped working. That matters when you decide whether this is an emergency or just a bad morning.
What Microsoft has confirmed
Cybersecurity News quoted Microsoft's notice: Microsoft is "investigating an issue in which some admins may be unable to access the Exchange admin center (EAC) and may encounter an 'Internal Server Error' message". Microsoft has directed customers to the Microsoft 365 admin center for more information.
A third-party status mirror that copies Microsoft 365 service-health data adds some detail:
- Incident ID: EX1500900
- Title: "Some admins may be unable to access the Exchange admin center (EAC)"
- Start time: Monday, October 12, 2026, at 09:35 UTC
- Scope (Microsoft's wording): impact "may be specific to any admin attempting to access the EAC," and Microsoft says this may change as the investigation continues
- Next scheduled update: 11:30 UTC. That time had already passed when this article was written, and the mirrored text still listed the incident as ongoing.
The scope wording describes who could be hit. It doesn't mean every admin in every tenant is locked out. The incident text gives no affected regions, tenant counts, root cause, workaround or resolution time.
In short: this is a confirmed portal-access incident with a known ID and an unknown cause. No timeline has been given.
The rollback claim: reported, not yet confirmed
Windows Report says the company has already started rolling back a recent change to the Exchange admin center. It adds that Microsoft says the rollback should help determine whether the change is responsible for the reported impact. The outlet also notes that the company has not confirmed that the issue is resolved, and its investigation remains ongoing.
The service-health text we could check doesn't mention a rollback yet. The mirrored update says Microsoft is reviewing service logs and diagnostic data to find the source of the problem. Those two accounts could fit together: the rollback may have come in a later update, or the mirror may not have picked it up. Either way, treat the rollback as Windows Report's account, not a documented fix. Cybersecurity News also points out that the notice doesn't name a root cause, and those gaps mean the incident should not be described as a cyberattack or linked to a specific service change.
If a rollback really is underway, it would point to a recent EAC deployment rather than a backend failure in Exchange Online. That's an inference until Microsoft's post-incident notes say so.
What admins should do right now
1. Check that you're seeing this incident, not a local problem
Administrators should check Health > Service health in the Microsoft 365 admin center and look for EX1500900. Microsoft Learn says to:
- Sign in to the Microsoft 365 admin center with an admin account.
- Go to Health > Service health, or click the Service health card on the Home dashboard.
- Under Active issues Microsoft is working on, click the incident title. The detail page shows every update Microsoft posts while it works on the problem.
Microsoft Learn also says people with the Service Support admin and Helpdesk admin roles can view service health. So your helpdesk can watch the incident without being given Exchange admin rights.
2. Subscribe to updates
On the incident page, choose Manage notifications for this issue to get email updates for EX1500900 alone, with up to two addresses per admin. Microsoft also suggests the Microsoft 365 Admin mobile app, which sends push notifications.
3. If you can't get into the Microsoft 365 admin center either
Microsoft Learn points admins to its public service status page and the @MSFT365status account on X. Windows Report says the first public confirmation of this incident came from that X account.
4. Find out whether mail is actually affected
The EAC is a management tool. When it fails, mail delivery doesn't fail with it. Cybersecurity News says the notice does not establish a global outage or confirm that users are unable to send and receive email. If users are reporting delivery problems as well, look for a separate Exchange Online incident in Service health instead of assuming it's part of EX1500900.
What not to treat as a fix
Most "Exchange admin center 500 error" results on the web don't apply here. Many cover on-premises Exchange Server 2010–2016, where HTTP 500 errors on ECP or OWA come from IIS configuration, virtual directories or missing arbitration mailboxes. Those fixes do nothing for a service-side problem in Exchange Online.
There are also older Exchange Online cases with their own workarounds. In a Microsoft Q&A thread from last year, about one admin's long-running 500 error, the suggested steps were checking different browsers or private mode, trying an alternate admin URL, and confirming the account still held the right Exchange roles. Cybersecurity News mentions an earlier EAC outage, EX1051697, where reports of an alternative portal address helping some administrators surfaced. The outlet is clear that those earlier findings do not establish a working fix for EX1500900.
Trying a private browser window does no harm. Just don't expect it to beat a service-side fault, and don't log it as a fix.
If you have urgent work, such as a delivery investigation or a mailbox change, you can fall back on your own contingency procedures. Exchange Online PowerShell is one example. Microsoft hasn't named any alternative as a mitigation for this incident, and it's not confirmed whether other management paths are affected.
A busy stretch for Microsoft 365 admins
The same status mirror shows how this fits into recent weeks:
- Earlier today (October 12), 07:00 UTC: a separate incident stopped some users from accessing or protecting content with Azure Rights Management. The mirror showed it resolved before the EAC incident.
- October 5: some admins intermittently couldn't reach the Microsoft 365 admin center, in certain regions.
- October 8: mail from on-premises Exchange servers to Exchange Online intermittently failed for some users.
None of these is shown to be connected to EX1500900. But this is the second admin-portal access incident in a week. That's why your monitoring shouldn't rely only on the portals Microsoft runs: email alerts and the mobile app keep working when a web console doesn't.
Bottom line
As of 13:00 UTC on October 12, 2026:
- Confirmed: some admins may get an "Internal Server Error" when opening the EAC. Microsoft is tracking this as EX1500900, which started at 09:35 UTC.
- Reported but unverified: Windows Report says Microsoft is rolling back a recent EAC change to test whether it caused the problem.
- Unknown: cause, affected regions, number of tenants, workaround and resolution time.
- Not supported by evidence: a mail-flow outage, a cyberattack, or a confirmed fix.
Keep an eye on EX1500900 in Service health and set up notifications. Don't spend the afternoon applying old on-premises IIS fixes to a cloud console. The final word on cause and recovery will come from Microsoft's own incident updates.