Continuing the discussion from Translate "Outlook 365" reactions into Discourse reactions:
Since Discourse cannot process Outlook reactions at this time, we can add a header to suppress Outlook clients from sending them.
According to @trs80 and How to Disable Outlook reactions - o365info,
This will reduce noise from Outlook users on Discourse forums.
In the future if we add support for them, we can remove the suppression header from topic emails.