Explanation/Reference:
Explanation:
Domain Security is a feature of Exchange Server (both 2010 and 2013) that can secure SMTP traffic between two Exchange organizations.
It is implemented on server level, and it works without configuring any options on user (sender or recipient) side. Domain Security uses mutual TLS authentication to provide session-based authentication and encryption.
Mutual TLS authentication is different from TLS as it is usually implemented. Usually, when you implement TLS, client will verify the server certificate, and authenticate the server, before establishing a connection.
With mutual TLS authentication, each server verifies the connection with the other server by validating a certificate that's provided by that other server, so clients are not included at all.
We establish secure SMTP channel between two Exchange Servers, usually over the Internet.
Clients, Outlook and Outlook Web App, will be aware that Domain Security is established.
Green icon with check mark will be shown on each messages exchanged between servers on which Domain Security is implemented.
The Set-SendConnector cmdlet is used to modify a Send connector.
The RequireTLS parameter specifies whether all messages sent through this connector must be transmitted using TLS. The default value is $false.
The DomainSecureEnabled parameter is part of the process to enable mutual Transport Layer Security (TLS) authentication for the domains serviced by this Send connector. Mutual TLS authentication functions correctly only when the following conditions are met:
The value of the DomainSecureEnabled parameter must be $true.

The value of the DNSRoutingEnabled parameter must be $true.

The value of the IgnoreStartTLS parameter must be $false.

The wildcard character (*) is not supported in domains that are configured for mutual TLS

authentication. The same domain must also be defined on the corresponding Receive connector and in the TLSReceiveDomainSecureList attribute of the transport configuration.
The default value for the DomainSecureEnabled parameter is $false for the following types of Send connectors:
All Send connectors defined in the Transport service on a Mailbox server.

User-created Send connectors defined on an Edge server.

The default value for the DomainSecureEnabled parameter is $true for default Send connectors defined on an Edge server.