Several Outlook users have reported the error Cannot start Microsoft Outlook window, Invalid XML, which they encounter while trying to start Microsoft Outlook on ...

Microsoft has fixed a known issue affecting Outlook for Microsoft 365 users since June and causing slow starts and freezes as if Offline Outlook Data Files (OST) were syncing right after launch.

Microsoft has admitted that an issue in Windows 11 24H2 could stop Outlook from starting. It has also been confirmed that Microsoft 365 Enterprise users will switch to the new Outlook in April 2026.… ...

Microsoft is working to address a known issue affecting Outlook for Microsoft 365 customers, causing slow starts and freezes as if Offline Outlook Data Files (OST) are being synced right after launch.