Two local domain with two different exchange

I am trying to set up a test lab where I create two different local domain (they are not public to Internet) and each of them have an exchange server.

For Example: DC01.local and DC02.local

What I am trying to do it might be simple but I do not have the knowledge to do it: I want, using this local environment, my exchange servers to send emails each other without using any public domain o ip address.

Is this possible? If so, what should I do to do it?

Thank you in advance,