mailer4.zenter.is has no NS records.
NS records for this zone are defined at zenter.is.
NS records for this zone are defined at zenter.is.
Question and response
Question
dig mailer4.zenter.is. NS
Answer
The response has no answer records.
Authority
zenter.is. 1800 SOA lia.ns.cloudflare.com. dns.cloudflare.com. 2395587190 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0