We currently have our IBM ISeries configured to send email thru our on premises Exchange 2013 server. The internal IP of the Exchange Server is 10.0.0.195 and I have a corresponding Host Table Entry on the ISeries pointing to that (10.0.0.195-MAIL.ROUTER.NAME). On the Exchange Server I have also setup a FrontEnd Receive Connector with the scope set to the internal IP of the ISeries (10.0.0.254). Everything works well and has for years.
However, we will be moving from hosting our Exchange on premises to using Rackspace's hosted Exchange and I was unsure how to route the email from the ISeries to Rackspace?