smtp.lx4.zetosa.com.pl has no NS records.
NS records for this zone are defined at zetosa.com.pl.
NS records for this zone are defined at zetosa.com.pl.
Question and response
Question
dig smtp.lx4.zetosa.com.pl. NS
Answer
smtp.lx4.zetosa.com.pl. 43200 CNAME mail.lx4.zetosa.com.pl.
Authority
lx4.zetosa.com.pl. 10800 SOA ns1.lx4.zetosa.com.pl. postmaster.lx4.zetosa.com.pl. 2010092900 28800 900 2419200 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0