I want my Sun Java System Messaging Server to forward all the incoming mails to some different host (without having a copy in data stores).
In Sendmail, we can do this by specifying DS[ip_address] in sendmail.cf file.
(Often referred as smart host).
This is not what a smarthost
is doing, unless you mean that you want to route the outgoing
mail to some third party mailserver.
In this case maybe the following could help, as I've used JES till version 6.3, so if something hasn't changed dramatically after the acquisition by Oracle the instructions should be the same.
To configure a smarthost, you should edit imta.cnf (make a backup first), find the line with the tcp_local channel definition, after "channel definitions" (or something like that) and add a daemon keyword followed by the hostname or the IP of the smarthost at the end of it. The whole tcp_local channel should look something like that:
tcp_local smtp mx ... daemon smarthost.domain.com
You can enclose the smarthost hostname or IP in brackets if you don't want to do a dns lookup.
After that you need to recompile the new configuration and reload: