Outlook: Improved handling of disallowed and failed email reactions

Outlook will improve handling of the x-ms-reactions: disallow header in Classic Outlook for Windows by disabling the Reactions button when reactions are disallowed and reverting failed attempts. This update, rolling out May-June 2026, ensures consistent behavior and reduces user confusion without requiring action. 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: Public Preview (Worldwide): We will begin rolling out early May 2026 and expect to complete by late May 2026. General Availability (Worldwide, GCC, GCC High, DoD): We will begin rolling out early June 2026 and expect to complete by late June 2026. 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: 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. Compliance considerations: No compliance considerations identified, review as appropriate for your organization. The Reactions button will appear grayed out when reactions are disallowed. View image in new tab 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. Learn more: Disallow reactions in Outlook | Microsoft Learn Message ID: MC1261593

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