Lean manufacturing depends on perfection. Every activity is well defined. Not only the work, but the way it has to be carried out is defined. Every responsibility is well identified. Therefore if you are a lean manufacturer you will ideally see only one address in your email under TO field and none in the CC list. Reason is you will be doing something well defined and you have the full responsibility of that activity. There is no need you to tell someone else what you are doing, when he is not directly involved in your activity. Long CC lists creates confusion. Responsibility is not focused and it is scattered. This will create a process where everyone is overloaded with information yet no one is actually responsible for the actions they take. Obviously this can not be a lean manufacturing system.
Emails and other forms of e communication is widely used allover the world. I am sure you do use emails everyday. I found an interesting fact sometime back when I studied few suppliers for an organization. Some emails contained many, many addresses in the CC list of the email. Then I found out these organizations are not performing well and associated with many problems like delays and quality problems.