Domino Directory contain users with @domain1.com and @domain2.com internet addresses. They both have the same Organization certifier and Domino Domain.
Domino Directory is replicated between all Domino servers.
All user mail files are located in Domino Mail Cluster.
Two Domino servers located in DMZ - Gateway1 and Gateway2. They don't have mail file replicas and are used to route emails to Internet and vice-versa.
Customer want that all emails sent from @domain1.com users should be routed to Gateway1 server and emails from @domain2.com users should be routed to Gateway2 server.
in postfix there is an option to route email based on sender address as mentioned above.
It would be nice if Domino could have such option.