Sorry, I had a break with this project as I still havent figured it out :/ There is something with the setup as Igor says. Please let me know if you have a solution.
Thank you for your reply. The domain zone for suni.sc is already setup correctly through Plesk Panel. I forgot to post the zone file.
This is what I can´t understand. The /etc/named.conf and zone file for suni.sc was checked for errors with named-checkconf and named-checkzone...