mx01.messages5.com has no NS records.
NS records for this zone are defined at messages5.com.
NS records for this zone are defined at messages5.com.
Question and response
Question
dig mx01.messages5.com. NS
Answer
The response has no answer records.
Authority
messages5.com. 900 SOA ns1.acoustic-adm.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0