Users of classic Microsoft Outlook are reporting widespread issues following the installation of the January 13, 2026, Windows 11 security update, KB5074109. The update, intended to improve system security, is instead causing Outlook to freeze adn remain running in the background, preventing restarts and, in some cases, leading to lost email data [[1]]. Microsoft has acknowledged the regression, notably impacting those utilizing the POP protocol, and is working on a resolution.
A recent Windows 11 security update is causing significant issues for users of the classic Microsoft Outlook, resulting in application crashes and unresponsive processes. The update highlights the ongoing challenges of balancing security patches with application stability in complex software ecosystems.
Update KB5074109, released on January 13, 2026, as part of the monthly security updates, is causing an endlessly running OUTLOOK.EXE process for many users. Even after closing the program window, the process remains active in the background, preventing the client from restarting and forcing users to manually end the process through Task Manager or reboot their entire computer to regain access to their email. Users are also reporting disappearing sent emails and completely frozen program windows.
The update was intended to deliver standard security patches and quality improvements for Windows 11. Instead, it triggered a regression specifically impacting Outlook’s session management. Users of the classic desktop version who manage their email accounts via the POP protocol (Post Office Protocol) with locally stored PST files are particularly affected. In these cases, the process doesn’t terminate correctly when the application is closed, leading the operating system to incorrectly assume Outlook is still running and blocking a restart.
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Is Outlook remaining in the background after the update, or are you noticing missing sent emails? Microsoft has officially acknowledged the problem as “under investigation” and published a corresponding support warning. While a permanent patch is still under development, engineers are working on a solution.
Affected users have several workarounds to restore functionality:
- Uninstall the update: The most reliable solution is to remove the faulty update through
Settings > Windows Update > Update History > Uninstall Updates. - Manually end the process: The
OUTLOOK.EXEprocess can be terminated via Task Manager (Ctrl+Shift+Esc) after closing Outlook, allowing the application to restart. - Switch to the web version: Outlook on the web (OWA) is not affected by the bug and provides a functioning alternative.
- Pause updates: Until a permanent fix is available, users should temporarily suspend automatic Windows updates.
The issue isn’t limited to Outlook. KB5074109 also introduced errors with Remote Desktop Connections, system shutdowns, and random screen crashes. Microsoft has already released emergency updates for some of these problems, but a specific fix for the Outlook bug was not available as of January 19.
Quality Control Under Pressure
This incident is part of a growing trend of Windows updates unintentionally impacting application stability. It underscores the dilemma for IT administrators: the need to deploy security updates promptly versus the risk of introducing new, productivity-hindering bugs.
For organizations, this serves as a reminder of the importance of a staged update management approach. By initially testing patches in a controlled environment, these types of issues can be identified before affecting the entire workforce. Users must now wait for a corrective update from Microsoft, which is expected to be released as an out-of-band patch or in the next monthly update.
