mx.rpmclassiccar.com has no NS records.
NS records for this zone are defined at rpmclassiccar.com.
NS records for this zone are defined at rpmclassiccar.com.
Question and response
Question
dig mx.rpmclassiccar.com. NS
Answer
The response has no answer records.
Authority
rpmclassiccar.com. 3600 SOA dns.rpmclassiccar.com. hostmaster.rpmclassiccar.com. 1859828868 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0