EnterpriseTechnology

Microsoft Windows 11 Update Freezes Outlook Classic – Fix

The January 13 2026 Windows 11 security update (KB5074109) breaks Outlook Classic for users with POP3 accounts and PST files, causing freezes, hung drafts, and blocked mail flow. Microsoft confirms the issue and provides a temporary fix: disable the Outlook Data Access feature or uninstall the KB5074109 update until a permanent patch is released.

What’s Causing Outlook Classic to Freeze?

The problem originates from the Windows 11 security update identified as KB5074109. After installation, Outlook Classic—Microsoft’s legacy client that supports POP3 and local PST storage—begins to hang, stop sending or receiving mail, and lose draft content.

Affected Update: KB5074109

  • Released on January 13 2026 as part of the Patch Tuesday rollout for Windows 11 24H2 and 25H2.
  • Targets security hardening but introduces a regression in how Windows handles PST file I/O.
  • Impact limited to Outlook Classic; Outlook for Microsoft 365 remains unaffected.

Temporary Workaround to Restore Outlook

Disable Outlook Data Access Feature

Microsoft’s immediate recommendation is to turn off the component that interacts with Outlook data files:

  1. Open Turn Windows features on or off from the Control Panel.
  2. Locate Microsoft Outlook Data Access and clear the checkbox.
  3. Restart the computer. Outlook should function normally, though the specific security enhancements tied to the feature will be disabled.

Uninstall the Problematic Update

If the issue persists, remove the update entirely:

  1. Go to Settings > Update & Security > Windows Update.
  2. Select View update history and click Uninstall updates.
  3. Find KB5074109 in the list and uninstall it.
  4. Reboot the system. Outlook will return to normal operation, but the machine will no longer have the security patches delivered by that update.

Technical Background

Outlook Classic stores email locally in PST (Personal Storage Table) files, a design favored for offline access and low‑bandwidth environments. The KB5074109 update modifies Windows’ file‑locking and indexing mechanisms, causing conflicts with PST file handling during background scans or backup processes. This regression leads to the observed freezes and data loss.

Impact on Users and Enterprises

  • Productivity loss: Stalled email sending/receiving and frozen drafts disrupt daily workflows.
  • Data risk: Unrecoverable drafts and potential PST corruption increase the chance of data loss.
  • Enterprise exposure: Organizations still deploying Outlook Classic for legacy systems face operational risk and must weigh the security implications of rolling back the update.

Next Steps and Recommendations

  • Apply the temporary workaround (disable Outlook Data Access) as the first line of defense.
  • If stability does not improve, uninstall KB5074109 while monitoring for an official Microsoft patch.
  • Back up PST files regularly to mitigate data‑loss scenarios.
  • IT teams should assess the security trade‑off of keeping versus removing the update and plan for a controlled rollout of the forthcoming fix.

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