What is the best way to set up a bunch of two mail servers Exchange and GMail?

Question

gmail

Good afternoon community!
I beg you to share your experience. There is a goal: to have two different mail servers for different categories of users on the same domain.

• A large but less active part of users (students) will use GMail.
  
• A smaller but very active part of users (employees) will use Exchange, which will be located inside the corporate network.
  

What are the ways to organize this? Make Exchange primary, and redirect letters to non-existent exchange recipients to gmail? Is it possible to do the opposite? Is it possible to implement fault tolerance with both schemas and two MX records with different weights?
Are there good manuals?
I ask for advice!

Answer 1

Tell me, what is the meaning of "we will not give students an exchange"? Are there that many?
just in case, a rather useful article about coexistence.
habrahabr.ru/post/227203