smtp.servperso.com has no NS records.
NS records for this zone are defined at servperso.com.
NS records for this zone are defined at servperso.com.
Question and response
Question
dig smtp.servperso.com. NS
Answer
The response has no answer records.
Authority
servperso.com. 1800 SOA bingo.ns.cloudflare.com. dns.cloudflare.com. 2396784086 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0