Now I can use message passing to send a message to you *directly* and indeed, that's "like email". For one-to-one correspondence, that's enough.
But it's not enough for a followers/following type mechanism. But we can build it on top! Thank *you* computational abstractions!
On top of "message passing" we will build "publish-subscribe" as a second-layer abstraction
"Your ideas are interesting and I'd like to subscribe to your newsletter."
You send me a letter saying you'd like to hear the things I have to say, okay, you're part of the reader list. That's how it works.