Illustration of how Erlang's mailbox works.

mailbox.erl

-module(mailbox).
-export([receiver/0, receiver_ordered/0]).

receiver() ->
    receive
        stop -> io:format("Stopped.~n");
        Msg  -> io:format("Message received: ~s~n", [Msg]),
                receiver()
    end.

receiver_ordered() ->
    receive
      {first, FirstString} ->
          io:format("First Message: ~s~n.", [FirstString])
    end,
    receive
      {second, SecondString} ->
          io:format("Second Message: ~s~n.", [SecondString]),
          receiver_ordered()
    end.