Email control system

Hi everyone!!

I'm in the need to find a system that will allow me to control emails in an enterprise.
The problem is as follows:

A user writes an email to a customer/provider. Before this email leaves the mail server (located at the office), it has to be checked (revised) by a head of department, and then by a head of division. If the mail is correct, then the email can leave the server torwards it's destiny. If it's not, it is returned to the original user (it may be rejected by eather one of the heads of department/division).
I know that Exchange does not allow this to be done but, is there a way to do this in any other way?
I'll be more than happy to give out more details if needed.

Thank you for reading!! :)