IP Networking

I am trying to install a replacement mail server. On the old machine,
nslookup example.com returns 192.168.100.5 instead of its real ip of 207.139......
On the new machine, which I have presumably set up the same way; I compared the data in the gui dnsconfig on both machines, I get an error message
;; got SERVFAIL reply from 192.168.100.6 trying next server

and then returns the external IP address.
The old machine is SUSE11 sp1 and the new machine is SUSE11 sp3.
If I lookup an external name on the new machine, I get the correct response from 192.168.100.6

---------- Post updated 11-09-15 at 12:09 AM ---------- Previous update was 11-08-15 at 11:03 PM ----------

Fixed. My eyesight is going. Dots at the end of the domain name are hard to see and very important.