I’m finding the explanation of messages rather poorly written.
First, you say that there are three part to a message: sender, target, and arguments. But what about the name of the message itself?
The example “mailer deliver” ends up printing the same address as “mailer” but there are three messages involved. The first message is “mailer deliver” and the second message is postOffice packageSender and the third message is “call sender”. (I assume)
Which of the three messages is mailer the sender? All of them? The first one?
You say that “call” is a method so “sender” is an argument?