My employer uses Outlook/Exchange and those reactions are a lot less annoying than short mails expressing the same thing on mailing lists and also is an alternative to notes not really demanding a proper response ending in the void. (Like a fun/life sharing post)
I don’t see any issues with it using outlook either but from what it sounds like when people do it for emails not managed by outlook, they’re getting a whole new email about it? If so, I could see how that would be annoying.