Microsoft is investigating widespread reports that a January Windows 11 security update is causing the classic Outlook desktop client to freeze and hang for users with POP email accounts.
POP (Post Office Protocol) is an email retrieval protocol used for downloading emails from a server to a local device. While POP isn’t as widely used as IMAP or Exchange, it is still popular among home users and small businesses.
This known issue affects users who have installed the KB5074109 security update for Windows 11 25H2 and 24H2, with those impacted reporting that classic Outlook does not exit properly and will not restart after being closed.

