mx1.value-domain.com has no NS records.
NS records for this zone are defined at value-domain.com.
NS records for this zone are defined at value-domain.com.
Question and response
Question
dig mx1.value-domain.com. NS
Answer
The response has no answer records.
Authority
value-domain.com. 1800 SOA gabriel.ns.cloudflare.com. dns.cloudflare.com. 2396971758 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0