  # Accept if the source is local SMTP (i.e. not over TCP/IP). We do this by
  # testing for an empty sending host field.
  accept  hosts = : +whitelisted_hosts_by_ip

  #
  # Don't bother doing an RDNS lookup for hosts in the RFC1918 ranges (makes
  # tests much faster).
  #
  accept  hosts = +private_addresses : +whitelisted_hosts_by_hostname

