mx.rackanddata.com has no NS records.
NS records for this zone are defined at rackanddata.com.
NS records for this zone are defined at rackanddata.com.
Question and response
Question
dig mx.rackanddata.com. NS
Answer
The response has no answer records.
Authority
rackanddata.com. 38400 SOA authns1.rackanddata.com. domainadmin.rackanddata.com. 1375326455 10800 3600 604800 38400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0