Soon after they launched Outlook Reactions in 2022, Microsoft received requests to disable the feature. Now you can by adding SMTP headers to messages. Outlook clients will be able to add the header to stop recipients reacting and organizations will be able to create mail flow rules to add the header to selected messages. It’s nice to have a way to disable reactions.
https://office365itpros.com/2023/09/19/outlook-reactions-disable/
