If I deliver a bunch of bytes at jet@spiegel.com then that's the destination. Now you can decrypt it with your public key and get `Have a nice day. Regards, so

If I deliver a bunch of bytes at jet@spiegel.com then that's the destination. Now you can decrypt it with your public key and get `Have a nice day. Regards, sobani` and see that I'm the sender. If I'm worried about leaking my IP address, I can use something like Tor. I'm confused why you think the sender needs to be known in any way to allow bytes to be delivered to your mail server.