Rules for multiple emails.

You'll probably do better doing three things:
1) Tell the people who work for you that they should only cc you when it's important and they should save up their emails a bit so they're not sending 50 per day. If they make their emails longer but there are fewer of them, that should cut some of the noise.
2) Another thing to do is use a team communications management system like Basecamp, Asana, Flow, or Slack. For those times when you are working out the kinks in a project, use these systems. Save email for communications with people outside the team.
3) You can also train everyone to not send the same attachment back and forth unless it's been changed. If you send the attachment to A, and then tell A to send the attachment to B, you don't need to see the attachment again, right? So you don't need to be cc'd on that, or you can be cc'd on a second email which is just "I sent the attachment to B."