How do I Mitigate Unproductive E-mail Volume?

I am sorry to say you can't do anything about other people. Think of it from the employee's side. There are some Managers that want to be copied on everything. It is safer to send e-mails then hold back. Be very careful. Employees are spiteful. If you bark at your people and say stop copying me, you will miss something important, as they will cut you off from everything. Most people are all (copy everything) or nothing (leave you out of everything).

You can only control your behavior. Tips -
- read the first paragraph only. If no interest - delete.
-if you need to respond, respond immediately. Do not say, "I'll look at it later." If you get frustrated from your first review, you will just get more frustrated if you close it to respond later.
-Train your people that you respond to e-mails once a day, let's say between 4 and 5pm. Tell them for important items, they should come to speak with you. Maybe they will reduce the e-mails if they realize you will not be looking at them until later.

Good luck.

Develop a methodology where you not only delegate but encourage autonomy.

Use project management/CRM software where items that would have normally gone to you as an FYI, goes to the system instead.

I agree with Regis on his last point (reading e-mail at specified times); because you now can focus on your work.

Have regular project/departmental meetings where you can go over the material that made its way to the project management/CRM system.