Dynamic CRM 2016 upgrade - System check error

Hi everyone, 

I am upgrading from Microsoft Dynamic CRM 2015 to 2016. When running the upgrade, I reach the "System Checks" screen and get an error under Microsoft Dynamics CRM Server User Input"

Error is: The specified computer that will be used for the Email Router cannot be found. Verify that the computer is available and try again"

Screenshot is attached.

Can you help me point to where this "computer" is specified?

I appreciate it

Thank you