mx.jlsimpson.com has no NS records.
NS records for this zone are defined at jlsimpson.com.
NS records for this zone are defined at jlsimpson.com.
Question and response
Question
dig mx.jlsimpson.com. NS
Answer
The response has no answer records.
Authority
jlsimpson.com. 3600 SOA dns.jlsimpson.com. hostmaster.jlsimpson.com. 1762896104 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0