Whilst I agree that email is the true universal standard I do not like how many mail providers and clients implement it badly. This then perpetuates issues with how people use it. I’m thinking things like to vs cc, reply all, etc. email etiquette, once gotten right is a great tool that helps both the sender and the receiver, without this email often has a lot of issues that can be frustrating to solve and lead to the rise in other tools (that are in themselves, silos).