Microsoft have implemented a way to turn off their awful reactions feature on emails that come from outside of Microsoft. While they should have made this an opt in not an opt out, my only way to handle this is to set the header x-ms-reactions: disallow
There isn’t a way to do this on a per account basis, but it appear that at least in their apps the reaction feature is “greyed out” and doesn’t allow a reaction. That’s not the case with their web app though which still allows them and sends an email to the sender with the reaction in it.