Introduction
Managing reactions in Outlook is evolving to improve user experience. Until now reserved for modern versions of Outlook such as Outlook Web App (OWA) and New Outlook, this functionality will soon be extended to classic Outlook. This update planned by Microsoft aims to standardize support for x-headers related to reactions across all Outlook clients.
Reactions in Microsoft 365: History and How They Work
Emoji reactions have been available in Outlook since October 2022. They offer a practical alternative to traditional replies by allowing automatic reactions with predefined emojis. Unlike Teams or Viva Engage, where adding custom emojis is possible, Outlook is limited to a restricted set fixed by Microsoft.
Reactions in Outlook are stored as MAPI properties ("MAPIReactionsBlob" and "ReactionsSummary"). These properties are not accessible via the Graph API, which limits detailed reporting on their usage.
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Good to Know
Classic Outlook was ignoring, until now, x-headers including reaction deletion rules. An update scheduled for June 2026 will correct this behavior.
Remove Reactions with a Transport Rule
Organizations wishing to prevent the use of reactions can configure a transport rule via Exchange Online. This approach prevents the use of reactions by inserting a specific x-header in emails.
Create a Transport Rule
Start by composing a transport rule via Exchange Online to manage reactions. Here is a PowerShell command illustrating this configuration:
1New-TransportRule –Name "Suppress Outlook Reactions" –Enabled $True –SetHeaderName "x-ms-reactions" -SetHeaderValue "disallow" -FromScope InOrganization –SentToScope InOrganizationImpact on Messages
Once the rule is applied, Outlook clients add the x-header to any incoming message. When it is displayed in classic Outlook, the disabled user interface prevents reactions.
Critical Point
X-headers are not universally compatible. Before the June 2026 update, classic Outlook will ignore this configuration, still allowing reactions.
Planned Improvements for Classic Outlook
Microsoft announced, via the Message Center (MC1261593), that a preview of this update will be available as early as May 2026. This evolution guarantees compatibility of classic Outlook with x-headers and standardizes the behavior of Outlook clients in environments such as GCC, GCC-High, or DoD by June.
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Impacts for IT Administrators
Administrators should expect visible changes in user behaviors:
- Reactions will be disabled for messages with the x-header.
- Perception of these changes will largely depend on the habits of users highly attached to classic Outlook.
Tip
To anticipate potential user feedback, prepare internal communication explaining the new rules for managing reactions in classic Outlook.
Conclusion
This update marks an important turning point in the Outlook universe by addressing the need for functional consistency in Microsoft 365. As an IT professional, consider analyzing the impact of reactions and adjusting your email management strategies accordingly.
