Exchange Server 2016 automatically configures Internet Information Services (IIS) virtual directories for web applications ...

Exchange Server 2016 automatically configures Internet Information Services (IIS) virtual directories for web applications such as %BRAND_EXCHANGE_ONLINE_SHORT% Web Services (EWS), Offline Address Book (OAB), %BRAND_OUTLOOK_WEB_APP_SHORT%, and %BRAND_EXCHANGE_ONLINE_SHORT% ActiveSync. In a hybrid configuration, the ExternalURL property for the EWS virtual directory must be configured with the externally accessible fully qualified domain name (FQDN) of your Internet-facing Exchange 2016 mailbox server. In this step you reset the external URL for virtual directories to the FQDN.