1. Setup AD DS's domain UNP suffixes so that multi domains can be used in Exchange Server
Go to 'Active Directory Domains and Trusts' -> Right click the top root on left tree pane -> Select 'Properties' -> Add 'Alternative UPN suffixes
2. Setup Exchange Server 2016
- Go to https://ExchangeServer/ecp
- Go to 'mail flow'
- Setup accepted domains', email address policies, receive connectors and send connectors
- Add recipients
Use MX record tracking online to to confirm the setup