_netblocks.megamailservers.com has no NS records.
NS records for this zone are defined at megamailservers.com.
NS records for this zone are defined at megamailservers.com.
Question and response
Question
dig _netblocks.megamailservers.com. NS
Answer
The response has no answer records.
Authority
megamailservers.com. 86400 SOA ns1.meganameservers.com. root.megamailservers.com. 509 86500 3600 3600000 345600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0