By default, no Send connectors exist for external mail flow when we install Exchange Server 2016. To enable outbound Internet mail flow, we need to create a Send connector, or subscribe an Edge Transport server to out Exchange organization.
We can create Send connectors in the Transport service on Mailbox servers, and on Edge Transport servers. Send connectors are stored in Active Directory and are visible to all Mailbox and servers in the organization.
To Create a Send connecter using EAC click on Mail Flow >> Send Connector
And then Click on + icon
Give send connecter a Meaning full name and select Internet in Type
On the next page, verify that MX record associated with recipient domain is selected.
This means the connector will use DNS on the Internet to route mail
On the Next page In the Address space section,
In the Fully Qualified Domain Name (FQDN), enter an asterisk (*), and then click Save.
This value indicates that the Send connector applies to messages addressed to all external domains.
Next The Scoped send connector,
This setting is important if you have Exchange servers installed in multiple Active Directory sites, if you keep it uncheck then all the exchange transport server in the organization are scoped by default to use this connecter, and If you select Scoped send connector, the connector is only usable by transport servers in the same Active Directory site.
Next in the Source server section,
Click icon. In the Select a Server dialog box that appears, select one or more Mailbox servers that you want to use to send mail to the Internet.
If you have multiple Mailbox servers in your environment, select the ones that can route mail to the Internet.
After you've selected at least one Mailbox server, click Add, click OK, and then click Finish.
Once we click finish we can see that we have send connector now available under Send Connectors.