Digital certificates are required for secure communications between on-premises Exchange 2016 servers, clients, and your ...

Digital certificates are required for secure communications between on-premises Exchange 2016 servers, clients, and your %BRAND_OFFICE_365_SHORT% organization. You need to obtain a certificate from a third-party trusted certificate authority (CA) and then install it on Mailbox and Edge Transport servers. Secure communications for internal connections between the on-premises Exchange 2016 Mailbox servers use self-signed certificates. We recommend that your certificate's common name match your primary SMTP mail domain (for example, contoso.com) for your organization. To learn more, see Certificate requirements for hybrid deployments.