Microsoft has released emergency out-of-band updates for Windows 10, Windows 11, and Windows Server to fix a problem that caused Microsoft Outlook to stop opening when PST files were stored in cloud services.
The issue started after Microsoft released the January 2026 Patch Tuesday updates. Since then, many Outlook users reported that the app would freeze or fail to open if their PST files were stored in cloud storage platforms such as OneDrive or Dropbox. In some cases, Outlook would only work again after users forced it using Task Manager or restarted their system.
A PST file in Microsoft Outlook is used to store emails, calendars, and other data locally on a computer instead of on a mail server. These files are especially common in enterprise environments, where employees need offline access to email or reliable local backups of important messages.
Microsoft explained that after installing Windows updates released on or after January 13, 2026, some applications may become unresponsive when opening or saving files from cloud-backed storage. Outlook was one of the most affected apps in certain configurations, particularly when PST files were linked to OneDrive. Users also reported other strange behavior, such as sent emails not appearing in the Sent Items folder and older emails being downloaded again.
The company noted that the problem mainly affects classic Outlook, which is commonly used in enterprise setups and is not included with most home versions of Windows. This explains why many personal users may not have noticed the issue.
To fix the problem, Microsoft released emergency updates for several Windows versions, including Windows 10, Windows 11, and multiple Windows Server editions. These updates are available through Windows Update and the Microsoft Download Catalog, allowing affected users and system administrators to install them immediately.
Microsoft also mentioned that the earlier out-of-band fixes released last week are now included in these updates. Those earlier fixes addressed problems with Microsoft 365 Cloud PC access and issues that prevented some systems with Secure Launch enabled from shutting down or entering hibernation.
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For users who are not experiencing these Outlook or cloud storage issues, Microsoft says there is no urgent need to install the emergency updates. In those cases, it is safe to wait for the next optional preview update or the regular Patch Tuesday release next month, when the fixes will be included as part of the normal update cycle.
