The Transport Config section allows you to configure the IP addresses of all Internal SMTP Servers.
Internal SMTP Servers
Internal SMTP Servers must be configured to allow Exchange to correctly identify internal and external messages. All IP addresses (IPv4 and IPv6) of all Internal SMTP Servers must be specified.
Several Exchange anti-spam settings have different thresholds or options for messages which originate from internal or external sources. The classification of internal or external sources is based on this list of IP addresses. All messages originating from IP addresses on the Internal SMTP Servers list will be classified as internal, and messages originating from all other IP addresses will be classified as external.
The Internal IP Addresses list can include other SMTP Servers (not just Exchange servers) in your organization.
The external public IP addresses (not just internal IP addresses) of your organization's SMTP servers should also be included on this list.