Can someone please educate me as to what the differentiation is between past email protocols, messaging protocols, and these types of APIs? I'm starting to get

Can someone please educate me as to what the differentiation is between past email protocols, messaging protocols, and these types of APIs? I'm starting to get this sense that we are just moving towards a singular communications protocol and the name, e.g., email or chat, is simply a matter of UI design and layout and maybe even unnecessary simulation of behaviors and actions.