mx0.fr.colt.net has no NS records.
NS records for this zone are defined at fr.colt.net.
NS records for this zone are defined at fr.colt.net.
Question and response
Question
dig mx0.fr.colt.net. NS
Answer
The response has no answer records.
Authority
fr.colt.net. 600 SOA ns0.coltfrance.com. eudnsmaster.colt.net. 2016110800 21600 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0