Outlook freezes after the latest Windows update: what to do if you have PST on OneDrive

This week many Outlook users have found a problem as frustrating as it is unexpected: the classic desktop client is hung after applying the latest Windows security updates. Microsoft has recognized the failure and has published interim information on its Windows health panel, but the final solution still has no specific date.

The conflict has been especially detected in POP-based equipment and PST files saved in cloud services such as OneDrive. After installing the update identified as KB5074109 on Windows 11 (versions 25H2 and 24H2), some users have seen how Outlook is blocked, not re-opened unless the process is completed from the Task Manager or the computer is restarted, or strange behaviors such as that the emails are redownloaded or that the messages sent do not appear in the Items sent folder.

Microsoft describes the problem in its status panel for Windows 11 25H2, where it clarifies that "any application can become non-responsive or experience unexpected errors when opening or saving files in cloud-backed storage" and gives the example of Outlook settings that store PST in OneDrive, which can cause the application to not respond or not reopen without completing its process. You can read the official note on Microsoft's health panel here: Windows release health - Known issues.

The range is not limited to Windows 11: Microsoft indicates that problems have also been observed in Windows 10 and several issues of Windows Server, including Server 2019 and Server 2022. Several media that closely follow Microsoft's incidents have reported the failure and time solutions suggested by the company; for example, you can see more context in ZDNet and BleepingComputer: ZDNet, BleepingComputer.

As Windows and Outlook teams investigate, Microsoft has already suggested several temporary steps to avoid blocking or minimize its effects. Among the less intrusive options is using the web version of the mail to work with the messages until a final correction is published, or moving the PST files out of synchronized folders with OneDrive (or any other cloud service) to remove interference with local file access.

For those who prefer to return to the previous state, there is also an alternative to uninstall the problem update (either KB5074109 or the related KB5073724). This is done from the Windows Settings application, in Windows Update > Update History > Uninstall updates, and by clicking on "Uninstall" next to the corresponding entry. Microsoft offers documentation on the process of removing updates on its support: How to Uninstall Updates in Windows.

Important precautions: removing safety patches reduces the protection of your equipment from vulnerabilities that the patches themselves correct. Microsoft explicitly warns about the risks of uninstalling security updates, because it can leave devices exposed to malware and other attacks; it is something to ponder before doing so and, in corporate environments, coordinate with the security team or system manager. The Microsoft guide explaining these risks is available here: Understanding the risks: why you should not uninstall security updates.

If you decide to move your PST out of OneDrive, the idea is to place them in a non-synchronized local folder and then indicate to Outlook the new location of the data file. If you choose to use webmail temporarily, make sure you export or support important emails before any change in PST location, to avoid accidental losses.

The situation comes at a time when Microsoft has had to post updates outside the usual schedule to correct other regressions or stability problems, such as urgent patches for errors in credentials notices on remote connections or for teams with Secure Launch. This dynamic shows that when large-scale safety patches are deployed, unforeseen side effects may occur that affect daily workflows.

In short, if you are an Outlook user with POP accounts and use PST on OneDrive, the most prudent thing right now is to temporarily change to the web interface of the mail or move the PST files to a local location until Microsoft launches a final correction. If you choose to uninstall an update, do it with risk awareness and, in professional environments, coordinate the measure with the security team. We will keep track of the news and recommend you reinstall official updates as soon as Microsoft publishes a secure patch.