Outlook: Improved handling of disallowed and failed email reactions

Updated May 18, 2026: We have updated the timeline. Thank you for your patience.  Introduction We’re improving how Outlook respects the x‑ms‑reactions: disallow header in Classic Outlook for Windows. This update ensures that when reactions are disallowed, the Reactions button is correctly disabled and any failed reaction attempts are fully reverted. This provides a more consistent and trustworthy user experience across Outlook clients and prevents user confusion. This message is associated with Roadmap ID 558442. When this will happen: Current Channel: This change has rolled out as part of version 2904 (build 19929). Monthly Enterprise Channel: This change has rolled out as part of version 2904 (build 19929). Semi-Annual Enterprise Channel: This change will be rolled out as part of version 2904 (build 19929). How this affects your organization: Who is affected: Users running Classic Outlook for Windows Organizations that disallow email reactions using the x‑ms‑reactions: disallow header What will happen: The Reactions button will appear grayed out when reactions are disallowed. Failed reaction attempts will be automatically undone in the UI. Users will no longer see misleading reaction states. Behavior will be consistent across all Outlook clients. The change is enabled by default and respects existing configurations. What you can do to prepare: No action is required. You may optionally: Inform helpdesk staff about the improved reaction behavior to reduce potential user questions. Review internal documentation if you reference reaction controls or messaging headers. Continue using the x‑ms‑reactions: disallow header as you do today; existing configurations are fully supported. Learn more: Disallow reactions in Outlook | Microsoft Learn Compliance considerations: No compliance considerations identified, review as appropriate for your organization.