mx.colorbusline.com has no NS records.
NS records for this zone are defined at colorbusline.com.
NS records for this zone are defined at colorbusline.com.
Question and response
Question
dig mx.colorbusline.com. NS
Answer
The response has no answer records.
Authority
colorbusline.com. 3600 SOA dns.colorbusline.com. hostmaster.colorbusline.com. 1896443729 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0