setting a mail smarthost in exim on a Cpanel box

add a Router block to the end of /etc/exim.conf.local:

@ROUTERSTART@
            smart_route:
                driver = manualroute
                domains = !+local_domains
                transport = remote_smtp
                route_list = * host.name.of.smart.host.server

then run the scripts to update configuration and restart exim:

root@box:~$ /scripts/buildeximconf  
root@box:~$ /scripts/restartsrv_exim  

You’re done.