mx.solarwinds.com has no NS records.
NS records for this zone are defined at solarwinds.com.
NS records for this zone are defined at solarwinds.com.
Question and response
Question
dig mx.solarwinds.com. NS
Answer
The response has no answer records.
Authority
solarwinds.com. 600 SOA a1-139.akam.net. hostmaster.solarwinds.com. 2013093108 1200 600 1209600 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0