mx156.hostedmxserver.com has no NS records.
NS records for this zone are defined at hostedmxserver.com.
NS records for this zone are defined at hostedmxserver.com.
Question and response
Question
dig mx156.hostedmxserver.com. NS
Answer
The response has no answer records.
Authority
hostedmxserver.com. 900 SOA ns-1611.awsdns-09.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0