New-ReceiveConnector -Name RelayConnector -usage Custom -Bindings ’192.168.1.10:25′ -fqdn server.domain.com -RemoteIPRanges 192.168.1.20 -server MYEXCHANGESERVER -permissiongroups ExchangeServers -AuthMechanism ‘TLS, ExternalAuthoritative’

The easist way is just to run this command in powershell:

Where:
192.168.1.10:25 is the IP address of the Exchange server
192.168.1.20 is the ip of the clients how need access to relay
server.domain.com is you exchange server FQDN
MYEXCHANGESERVER is you exchange server hostname