sub.emailv.com has no NS records.
NS records for this zone are defined at emailv.com.
NS records for this zone are defined at emailv.com.
Question and response
Question
dig sub.emailv.com. NS
Answer
The response has no answer records.
Authority
emailv.com. 1800 SOA will.ns.cloudflare.com. dns.cloudflare.com. 2395684200 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0