mx.principalpipe.com has no NS records.
NS records for this zone are defined at principalpipe.com.
NS records for this zone are defined at principalpipe.com.
Question and response
Question
dig mx.principalpipe.com. NS
Answer
The response has no answer records.
Authority
principalpipe.com. 3600 SOA dns.principalpipe.com. hostmaster.principalpipe.com. 1197789885 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0