mx.celd.com has no NS records.
NS records for this zone are defined at celd.com.
NS records for this zone are defined at celd.com.
Question and response
Question
dig mx.celd.com. NS
Answer
The response has no answer records.
Authority
celd.com. 1800 SOA ben.ns.cloudflare.com. dns.cloudflare.com. 2396107102 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0