MICROSOFT has issued an emergency out-of-band patch to fix the instability in Outlook Classic caused by this month’s security updates, with the update being deployed automatically via Windows Update rather than requiring manual installation.
The article lists update identifiers and builds for several Windows editions, including Windows 11 25H2/24H2 (KB5078127, Build 26200.7628 / 26100.7628) and Windows 11 23H2 (KB5078132, Build 22631.6495), alongside Windows 10 22H2/21H2 (KB5078129, Build 19045.6812 / 19044.6812) and Windows Server 2025, 2022 and 2019 variants with their respective builds.
It notes that the underlying cause lies in a modification to cloud storage mechanisms and could affect any application attempting to save data to OneDrive, Google Drive or Dropbox. Users relying on Outlook Classic or cloud storage for data preservation are advised to ensure these updates are applied, as failures could lead to synchronization issues or data loss during cloud saves. The guidance emphasises verifying that system update functionality is active, since the patches are delivered automatically.