mx4.trellian.com has no NS records.
NS records for this zone are defined at trellian.com.
NS records for this zone are defined at trellian.com.
Question and response
Question
dig mx4.trellian.com. NS
Answer
The response has no answer records.
Authority
trellian.com. 86400 SOA ns1.trellian.com. hostmaster.trellian.com. 2026022000 14400 3600 604800 86400
Additional
. 0 OPT ; payload 512, xrcode 0, version 0, flags 0