Microsoft's October Update Breaks Exchange: What You Need to Know

Robert Moore · 2026-10-19

Microsoft just dropped a bombshell for IT admins: the October Windows Server security updates are breaking Exchange Server sign-in and mail flow for some organizations. If you're running Exchange on-premises or in a hybrid setup, you might have already noticed users can't access Outlook on the web (OWA) or emails aren't being delivered. This isn't a small glitch—it's a full-blown disruption that could leave your business scrambling. ### What Exactly Is Happening? According to Microsoft, the issue stems from the security updates released on October 10, 2023 (KB5031361 for Windows Server 2019 and KB5031358 for Windows Server 2022). These updates are causing authentication failures and mail delivery problems on Exchange Server 2019 and 2016. Specifically, users may see errors like "Something went wrong" when trying to sign in to OWA, and messages might queue up in the transport queue without being delivered. ### Who's Affected? Not everyone will hit this problem, but if you're running Exchange Server in a hybrid environment or have specific configurations, you're at risk. Microsoft hasn't provided a full list of affected configurations, but early reports suggest that servers with certain security settings or third-party integrations are more likely to experience issues. If your users are complaining about login failures or missing emails, you're probably in the affected group. ### What Should You Do Right Now? First, don't panic. Microsoft is aware of the problem and is working on a fix. In the meantime, here are steps you can take to mitigate the impact: - **Check your update status**: If you haven't installed the October updates yet, consider pausing them until Microsoft releases a patch. But be aware that skipping security updates comes with its own risks. - **Roll back if necessary**: If you've already installed the updates and are experiencing issues, you may need to uninstall them. Microsoft has provided guidance on how to do this, but proceed with caution—rolling back security updates can leave your system vulnerable. - **Monitor Microsoft's advisory**: Keep an eye on the official Exchange Team blog and Microsoft's health dashboard for updates. They're actively investigating and will likely release a fix soon. - **Communicate with your users**: Let them know what's going on and set expectations. A little transparency goes a long way in reducing frustration. > "We're seeing a significant uptick in support tickets related to Exchange authentication and mail flow since the October updates," said one system administrator on a popular IT forum. "It's a mess, but at least Microsoft is acknowledging it." ### The Bigger Picture: Why This Matters This incident is a reminder of the delicate balance between security and stability. Security updates are essential, but they can sometimes introduce unforeseen issues. For IT pros, it's a wake-up call to have a rollback plan and to test updates in a staging environment before deploying them broadly. And for businesses, it highlights the importance of having a resilient email infrastructure—whether that's a hybrid setup or a move to the cloud. ### What's Next? Microsoft hasn't given a timeline for a permanent fix, but they're typically quick to respond to such critical issues. In the meantime, stay informed, back up your data, and keep your users in the loop. We'll update this article as soon as more information becomes available. In the world of IT, surprises are part of the job—but this one's a doozy. Stay safe out there.