How to Disable Outlook Reactions

Stop People Using Graphic Reactions to Email

Preannounced in message center notification MC670444 (updated 6 September 2023, Microsoft 365 roadmap 117433), with further details provided in a post in the Microsoft Technical community on September 15, Microsoft is giving organizations a way to disable Outlook reactions. The server-side block is rolling out now and should be complete worldwide by the end of September.

Outlook reactions allow users to respond to messages with a graphic reaction using Outlook classic, the Monarch client, OWA (Figure 1), or Outlook mobile. The idea is that recipients can respond to message by selecting a reaction rather than typing out a reply. The mechanism is common in messaging systems like WhatsApp, Facebook, and Teams. Some people love using reactions, others think it’s an abomination on the face of email.

Responding to a message with Outlook reactions
Figure 1: Responding to a message with Outlook reactions

The Wish to Disable Reactions

Soon after Microsoft enabled Outlook reactions, tenant administrators looked for a way to disable the feature with appeals like this post in the Microsoft Technical community. Microsoft’s blog post says that soon Outlook users will be able to choose to “Disallow reactions” for new email. This option must be chosen when composing an email. Once the message is sent, its properties cannot be updated to disallow reactions. Microsoft says that OWA will get the ability to disallow reactions (Monarch should get the feature at the same time) followed by Outlook classic and the other Outlook clients.

The ability to disable reactions depends on being able to add and recognize the SMTP x-ms-reactions: disallow message header for an email. When the Exchange transport service sees this header on a message, it knows that it should block reactions. Likewise, when an Outlook client sees the header, it knows that it should disable the ability of the recipient to respond with a reaction. Of course, it will take time for all Outlook clients to block the ability of a user to react to a message. However, if a block exists and an older client allows someone to respond with a reaction, Exchange Online will suppress the reaction and won’t allow the sender to see the response.

Because an SMTP message header controls the ability of clients to respond with reactions, it’s possible to  construct mail flow rules to block reactions completely for outbound messages to external organizations or to selected domains. Figure 2 shows a mail flow rule to disable Outlook reactions for email delivered to external recipients.

A Mail Flow rule to disable Outlook reactions for outbound messages
Figure 2: A Mail Flow rule to disable Outlook reactions for outbound messages

eDiscovery and Outlook Reactions

Whether or not someone responds to a message with a reaction is an interesting clue for eDiscovery investigators. For instance, if you send me a message saying “Let’s commit fraud” and I respond with a thumbs-up reaction, it could be construed that I agree with the proposal to commit fraud.

Unfortunately, you can’t run an eDiscovery search for reactions. Instead, investigators must check the properties of message found by searches to verify the presence of any reactions. Examining message properties with the MFCMAPI program, an investigator can see if any reactions exist for a message. Figure 3 shows the reaction data in the MAPIReactionsBlob property.

Outlook reactions data stored in the MAPIReactionsBlob for a message
Figure 3: Outlook reactions data stored in the MAPIReactionsBlob for a message

Microsoft notes that the way the MAPIReactionsBlob property stores reaction information is “not memory efficient” and that the same data is available in the ReactionsSummary property. I’m sure that they’re right, but the data in the ReactionsSummary property is encoded and less accessible than the information in MAPIReactionsBlob. This situation might change as Microsoft renames the ReactionsSummary property to OwnerReactionHistory.

Disabling is a Tenant Choice

Microsoft often comes up with ideas to enhance Outlook and other clients that work well for some tenants and not for others. With around 400 million paid seats, Office 365 is a broad church, which means that new features that change client UIs are best when they come with the ability to disable the feature. It’s taken a while to disable Outlook reactions, but at least it’s now possible.

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