Domino SMTP IN server configuration

We have two Domino mail servers in Active-Passive clustered mode.We also have one Domino SMTP IN server and one Domino SMTP OUT server.What should be the IP that we will give on “Relay host for messages leaving the local internet domain” field of Domino SMTP IN server? Should we give the IP of both the Domino mail servers?If we give the IP of both the mail servers will there be any duplicacy of mails since mail files of all the users exist on both the Domino mail server(since it is in clustered mode).