mail.mlsend.com has no NS records.
NS records for this zone are defined at mlsend.com.
NS records for this zone are defined at mlsend.com.
Question and response
Question
dig mail.mlsend.com. NS
Answer
The response has no answer records.
Authority
mlsend.com. 1800 SOA andy.ns.cloudflare.com. dns.cloudflare.com. 2395775749 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0