mx.bisonrow.com has no NS records.
NS records for this zone are defined at bisonrow.com.
NS records for this zone are defined at bisonrow.com.
Question and response
Question
dig mx.bisonrow.com. NS
Answer
The response has no answer records.
Authority
bisonrow.com. 3600 SOA dns.bisonrow.com. hostmaster.bisonrow.com. 1401193428 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0