For transport domain to another server use folowing script
create file /etc/staticroutes
in this file add domains with IP addreses or MX domain names
first1.com: IP or mx.new-server.info
second.com:IP or mx.new-server.net
next go to WHM > Exim Configuration Editor > Advanced Editor and locate the routers area, then put this into that routers box:
static_route:
driver = manualroute
transport = remote_smtp
route_data = ${lookup{$domain}lsearch{/etc/staticroutes}}