i agree reactions can be useful, but adding them to email the way Microsoft has is obnoxious for recipients using any client other than theirs. and, i think this is probably their intention: receiving an email reaction in a client that doesn't render it as a reaction feels wrong and MS probably hopes this will encourage some people to switch to using Outlook.

the right way to add reactions to email would be to make it opt-in (and also not a vendor-specific header but instead something which aims to become a standard): clients should only allow reactions to messages which contain a header signaling that the sender supports receiving them.

but email is used specifically for receipts, otherwise messaging would be used

I realize that this is up to the user and that choice is great, so the issue comes down to implementation. and as a user... I find out far after the fact that somebody reacted to my email because outlook doesn't show me those notifications in a timely manner, nor am I going to look for them because I consider that a chat feature and Microsoft already sends me enough notification spam

Better to read and don't reply, or send a message and expect it was received IMO

If it's worth replying, write a reply. I do not need a notification from anyone of a round asshole flashing different colors and gyrating because you casually agree in a congratulatory fashion.

Ok but the point is, if anyone isn't using Outlook they do get a pointless email. My workplace doesn't use Outlook and I get tons of these. I'm glad to have learnt I can block them though.