mail relay through smarthost on exim

To enable mail rely through smarthost, edit /etc/exim/exim.conf file.

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######################################################################
#                      ROUTERS CONFIGURATION                         #
#               Specifies how addresses are handled                  #
######################################################################
#     THE ORDER IN WHICH THE ROUTERS ARE DEFINED IS IMPORTANT!       #
# An address is passed to each router in turn until it is accepted.  #
######################################################################

begin routers

Add Below

smarthost:
driver = manualroute
domains = *
transport = remote_smtp
route_data = IP_OF_SMARTHOST_HERE

For my exim mail server running on LAN, i used

######################################################################
#                      ROUTERS CONFIGURATION                         #
#               Specifies how addresses are handled                  #
######################################################################
#     THE ORDER IN WHICH THE ROUTERS ARE DEFINED IS IMPORTANT!       #
# An address is passed to each router in turn until it is accepted.  #
######################################################################

begin routers

smarthost:
driver = manualroute
domains = *
transport = remote_smtp
route_data = 192.168.0.1

192.168.0.1 is IP of main PC that runs mail server.