Use the EAC to create a Send connector to route outbound email through a smart host
In the EAC, navigate to Mail flow > Send connectors, and then click Add .
In the New send connector wizard, specify a name for the send connector such as MailRoute Outbound and then select Custom for the Type. You typically choose this selection when you want to route messages to computers not running Microsoft Exchange Server 2013. Click Next.
Choose Route mail through smart hosts, and then click Add . In the Add smart host window, specify the fully qualified domain name (FQDN), outbound.mailroute.net. Click Save.
For Smart host authentication, choose None.
Under Address space, click Add . In the Add domain window, make sure SMTP is listed as the Type. For Fully Qualified Domain Name (FQDN), enter * to specify that this send connector applies to messages sent to any domain. Click Save.
Cost: Verify 1 is entered. A lower value indicates a more preferred route for the domains you specified.
* Back on the previous page, the Scoped send connector setting is important if your organization has Exchange servers installed in multiple Active Directory sites:
If you don't select Scoped send connector, the connector is usable by all transport servers (Exchange 2013 or later Mailbox servers and Exchange 2010 Hub Transport servers) in the entire Active Directory forest. This is the default value.
If you select Scoped send connector, the connector is only usable by other transport servers in the same Active Directory site.
When you're finished, click Next.
5. For Source server, click Add . In the Select a server window, choose a server and click Add . Click OK.
Once you have created the send connector, it appears in the Send connector list.
How do you know this worked?
To verify that you have successfully created a Send connector to route outbound email through a smart host, send a message from a user in your organization (you can use the Outlook Web App) to the domain you specified for the Address space. If the recipient receives the message, you've successfully configured the send connector.
For the original documentation from Microsoft please see here: