This is an old revision of the document!
https://www.techieshelp.com/exchange-2013-enable-anti-spam/
https://www.informaticar.net/exchange-server-whitelisting-domains-and-email-addresses/
https://blog.ahasayen.com/smtp-relay-exchange-internalsmtpservers/
https://docs.microsoft.com/en-us/Exchange/antispam-and-antimalware/antispam-protection/antispam-on-mailbox-servers?view=exchserver-2019
Get-TransportConfig | fl InternalSMTPServers Set-TransportConfig -InternalSMTPServers @{Add="<ip address1>","<ip address2>"...}