How to serve direct delivery for a particular domain along with a smarthost for rest

customdelivery:
  condition = ${if eq {${lc:$domain}} {themactep.com} {true} fail }
  driver = dnslookup
  transport = remote_smtp

or

customdelivery:
  condition = ${if eq {${lc:$domain}} {themactep.com} {true} fail }
  driver = manualroute
  transport = remote_smtp
  route_list = "* mail.themactep.com byname"

add this to /etc/exim4/conf.d/router/200_exim4-config_primary before smarthost entry.