Critical Bug Alert: Outlook Keeps Crashing on Windows 11, Microsoft Pushes Emergency Fix

Critical Bug Alert: Outlook Keeps Crashing on Windows 11, Microsoft Pushes Emergency Fix

Introduction

Millions of people rely on Outlook for email communication every day — especially on Windows 11. But recently, a severe bug caused Outlook keeps crashing on Windows 11 for countless users worldwide. Microsoft confirmed that a January security update introduced a regression leading to frequent Outlook crashes, forcing the company to release an emergency out-of-band fix outside the regular update cycle.

What Is the Outlook Crashing Issue on Windows 11?

The crisis started after Microsoft’s January 13, 2026 security update (KB5074109) was installed on many Windows 11 systems. Soon after, users reported that Outlook keeps crashing on Windows 11, especially when opening the classic Outlook client with local PST or POP accounts stored in cloud-sync services such as OneDrive.

Symptoms included Outlook failing to launch, freezing mid-use, or closing immediately after startup without warning. Many users also lost access to recently sent or received messages due to the unexpected behavior.

Who Is Affected by This Bug?

The Outlook crash issue primarily affected:

• Windows 11 versions 24H2 and 25H2 users on desktops and laptops.
• People running Outlook Classic with POP3 or PST profiles.
• Devices where PST files are stored in cloud-synced folders such as OneDrive or Dropbox.

By contrast, users who primarily rely on Outlook Web App or Exchange/IMAP profiles saw fewer problems. However, the crash issue was widespread enough that even enterprise environments were impacted.

Symptoms of the Outlook Crash Problem

Users experiencing the Outlook keeps crashing on Windows 11 issue reported:

• Outlook freezing or showing “Not Responding.”
• Outlook closing immediately after launch with error indicators.
• Sent emails not appearing in the Sent Items folder.
• Previously downloaded emails being unexpectedly re-downloaded.
• Outlook.exe remaining active in the background after closing.

These issues frustrated users and disrupted normal workflows, especially in corporate settings where email is crucial.

Root Cause: Why Outlook Crashes

Microsoft attributed the problem to an interaction between Windows 11 file-handling changes in the January security update and how Outlook manages PST files — particularly those stored in cloud-synced folders. The new code path altered file-I/O expectations and introduced race conditions that the legacy Outlook client wasn’t built to handle.

In plain terms, cloud sync clients like OneDrive change how files are accessed behind the scenes. When Outlook expects standard local file behavior, the altered API behavior from Windows 11 caused deadlocks, hang states, or crashes — hence the repeated Outlook keeps crashing on Windows 11 reports.

Microsoft’s Emergency Fix: What’s New

In response to intense user complaints and productivity loss, Microsoft released an emergency out-of-band cumulative update identified as KB5078127. This patch was developed outside the regular monthly update schedule to address the root causes of the Outlook crash issues.

The emergency fix is designed to:

• Repair cloud-file access regressions that led to Outlook crashes.
• Restore normal file I/O handling for PST files on Windows 11.
• Include previous security updates so users don’t have to uninstall the January security patch.

This update is available via Windows Update and the Microsoft Update Catalog for affected systems.

How to Fix Outlook Crashing on Windows 11 (Step-by-Step)

Method 1: Install the Emergency Update

1. Open Settings on Windows 11.
2. Go to Windows Update.
3. Click Check for updates.
4. Install any pending updates, especially KB5078127.

Method 2: Avoid Cloud-Synced PST Storage

Move your PST files out of OneDrive or similar folders to local storage (e.g., C:\Users<User>\Documents). This prevents Outlook from stumbling over altered cloud behaviors.

Method 3: Use Outlook Web

Switch temporarily to Outlook Web App if Outlook keeps crashing on Windows 11 until the fix is confirmed stable.

Method 4: Uninstall the January Update

If the issue persists, remove the January patch KB5074109 via Settings > Windows Update > Update history > Uninstall updates and roll back to a stable state. Note: this leaves security fixes undone.

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Has Microsoft Fully Resolved the Issue?

The emergency update significantly reduces the frequency of Outlook keeps crashing on Windows 11 incidents and restores email stability for most users. However, occasional edge cases may still occur, especially for legacy profiles or uncommon storage setups. Microsoft continues to refine the solution.

User Reactions & Impact

Tech forums and IT professionals highlighted frustration over disrupted productivity, lost time, and the need to apply emergency patches. Many users reported that their daily work stalled because Outlook keeps crashing on Windows 11, particularly when juggling large PST files or cloud sync.

What Should Users Do Next?

• Keep Windows Updated: Install the emergency update as soon as possible.
• Back Up PST Files: Ensure you have local backups in case of future problems.
• Track Official Announcements: Watch Microsoft’s support channels for ongoing fixes.

Conclusion

The widespread reports that “Outlook keeps crashing on Windows 11” triggered a swift emergency update from Microsoft. While the issue was serious and impacted users globally, the release of KB5078127 shows Microsoft’s ability to react quickly to critical bugs. If you’ve faced repeated Outlook crashes, install the latest update, move PSTs to local storage, and monitor further patches to keep your email experience stable and reliable.