smtp.gthost.com has no NS records.
NS records for this zone are defined at gthost.com.
NS records for this zone are defined at gthost.com.
Question and response
Question
dig smtp.gthost.com. NS
Answer
The response has no answer records.
Authority
gthost.com. 1800 SOA chip.ns.cloudflare.com. dns.cloudflare.com. 2397021433 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0