Isn't that the basis/point of the actor model? Actors can message each other and processing the message can trigger state mutation of the recipient, but they can't directly mutate each other.
All data is immutable on the BEAM with a few exceptions, so no mutation within actors.
No, that's not true. Actors in elixir/erlang mutate their state through tail call recursion through the loop function.
That's kind of what akka is on scala or java. Messages are immutable _BY CONVENTION_ but you can do whatever you want.