Microsoft is investigating a Windows 11 regression that is causing classic Outlook to hang, lag, or become unresponsive after the January 13, 2026 cumulative update (KB5074109).

Windows 11 Patch Tuesday updates for 24H2 and 25H2 reportedly break classic Outlook, causing freezes, hangs, and lost email drafts.

Microsoft confirmed that the KB5074109 January Windows 11 security update causes the classic Outlook desktop client to freeze and hang for users with POP email accounts.

Windows 11 KB5074109 causes a black screen on some PCs, including those with an Nvidia GPU, and also freezes Outlook if you use POP.

Windows 11 KB5074109 causes Outlook freezing for POP accounts. Microsoft confirms the issue and investigates a permanent fix.

Microsoft has confirmed a known issue that prevents recipients from opening encrypted emails in classic Outlook.