In an outlook only company, reactions make a ton of sense. They save tons of "great, thank you " emails. Of course you can still send real thank you emails when you're genuinely thankful!
I literally had to set up a “Congratulations / Congrats” filter to auto-delete those emails because they were so frequent and numerous when various accomplishments across the org were announced. The party popper emoji at least makes that far more tolerable.
Is this just the sender looking for visibility? Does the recipient appreciate that yet another middle manager CC'd the whole company on a single sentence congratulatory message? Is there some other social function at work here that I don't understand?
Sometimes I think it would be funny if all the individual contributors coordinated to ALSO reply-all with "Congratulations", but it would become clear pretty quickly that something was up, and it's a mean thing to do to whomever is being congratulated.