I often say that the only reason email is in the form it is today is because it happened before corporate interests took over communication.
If it had been invented today you could only iMessage other iDevice holders. Maybe you would also have had another for-profit middleware company just to deliver messages between Apple and Android devices. Something like a telephone exchange.
In one of the movies about Steve Jobs, he actually does want to make email proprietary and to only be able to send and receive emails on Macs. There was also talk (involving Bill Gates IIRC) about having an electronic stamp (basically a charge for email).
I very much agree, if it were invented today there's no way it would be an open standard. It almost wasn't even back then.