Reactions in Outlook: Public usability update September 2023

Thanks for the feedback! Here's a super sneak peek at the hover behavior for the grayed-out reaction button; this change should be deployed by next week. There will be an informative message that reflects the disallowed-ness:

The plan on record is to use the x-ms-reactions: disallow mail header for any and all grayout of reactions on all Outlook clients. The flexibility it provides is unparalleled:

1. Admins that want a blanket disallow can add Mail flow rules to that effect. For example, applying the header on inbound mail from "NotInOrganization" (as shown in the example in the post) would achieve a blanket disallow on all emails inbound from outside the tenant, for companies that want their employees to react to their colleague's emails but not their customers'.
2. Individuals that want a case-by-case disallow can use the checkbox UI when composing to disallow reactions; under the covers it stamps the header onto the outgoing email.
3. The disallowed-ness is recorded directly in the email's SMTP data, so admins can already start stamping emails now and take advantage of the server-side rejection of the reaction attempt even while waiting for the client-side updates to see the grayout.

There are no plans to introduce a toggle of some sort to control reactions in Admin Center. If that were to change in the future, it's a safe bet that it will simply make it easier to stamp the SMTP header.

The grayout is already live on the new Outlook for Windows; for the classic Desktop client, we're hoping to be able to make the change within the next few months.