Secure Sockets Layer (SSL) digital certificates help to secure communications between the on-premises Hub Transport servers ...

Secure Sockets Layer (SSL) digital certificates help to secure communications between the on-premises Hub Transport servers and your %BRAND_OFFICE_365_SHORT% organization. If you're already using digital certificates in your %BRAND_EXCHANGE_ONLINE_SHORT% organization, you may have to modify the certificates to include additional domains or purchase additional certificates from a trusted certificate authority (CA). If you aren't already using certificates, you will need to purchase one or more certificates from a trusted CA. Learn more at Certificate requirements for hybrid deployments.