[exim] Mail delivery failing to internal/rfc1918 hosts

I've just setup a Debian lenny box running Exim 4.69. All works fine,
except I can't get Exim to deliver mail to my internal Exchange server
which has a 192.168.x.x address. I read about the ignore_target_hosts
option in /etc/exim4/conf.d/router/200_exim4-config_primary, but have it
commented out. I've restarted Exim, but Exim still refuses to deliver
mail.

In /var/log/exim4/mainlog, I see the following error:

"all relevant MX records point to non-existent hosts"

I've verified that DNS resolution is resolving the proper MX and that I
can manually telnet to port 25 on that MX from the command line of this
box. Mail delivery to other hosts on the general Internet is working
fine.

Thoughts?

--
Best regards,
Fred Weston, Network Operations
P: 386.274.6255 M: 386.843.0123
MCP+I, A+, Network+, Linux+, CCNA
Ladies Professional Golf Association