> That’s the case of any protocol

Well, E-Mail is inherently async and allows a sequence of relays with no back channel to confirm delivery.

With other protocols (except snail mail) I get a confirmation that recipient was valid and the message for delivered. With some I even get a marker it was read.

With e-mail, with luck, I get a cryptic not standardized response mail, if something went wrong. Sometimes even only a lot later as delivery is retried for a few days in some cases.