Microsoft has released an emergency Windows update (KB5078127) to fix a critical issue that left many Outlook users unable to launch the application after the company’s January 2026 security updates went live.
The problem first appeared after the January 13, 2026 Patch Tuesday updates, which were intended to strengthen Windows security but instead caused significant system instability and application failures. Affected users—particularly those with classic Outlook configurations that stored PST files in cloud-linked folders such as OneDrive or Dropbox—reported the app hanging, becoming unresponsive, or crashing on launch.
In response, Microsoft released the out-of-band update KB5078127 on January 24, 2026, which is now rolling out to Windows versions including 24H2 and 25H2. This emergency patch is designed to restore normal operation to Outlook and other affected applications that failed to open or behaved erratically after the initial updates.
📌 Key Highlights
- The update fixes the launch issues for Outlook that occurred when PST and POP files were stored in cloud-backed locations.
- It also addresses crashes and unresponsive behavior in other applications that rely on cloud storage integration.
- This is the second emergency patch Microsoft has issued in January 2026, following earlier fixes for shutdown, hibernation, and Remote Desktop failures.
- Some non-related bugs from the original update—such as File Explorer display issues—are expected to be resolved in the next scheduled update.
Microsoft recommends that users install KB5078127 if they are experiencing Outlook startup problems, though systems already running smoothly with January’s security patches may not need to update again.
The swift release of this emergency update underscores the importance of stability for essential productivity tools like Outlook, especially in corporate and business environments where email reliability is critical.