The following is Network Diagram of this example:

If you does not know how to build AD DS, you can view this post “Building AD DS for Lab “.

If you does not know how to install Exchange, you can view this post “Building Exchange Server for Lab “.

How to send email between 2 Exchange at different domain:

1. Create MX record at DNS at each domain

2. Create Conditional Forwarders at each domain

3. Confirm Default Frontend allow Anonymous

4. Create SMTP send connectors