Yeah SMTP relaying is quite common. The problem is due to email architecture, to my knowledge, that same relay is going to be able to read your incoming emails

Yeah SMTP relaying is quite common. The problem is due to email architecture, to my knowledge, that same relay is going to be able to read your incoming emails because remote servers will block emails from user@endserver.org sent from relay.net unless endserver.org has MX entries pointing to relay.net.