ns2.lublin.pl has no MX records.
Question and response
Question
dig ns2.lublin.pl. MX
Answer
The response has no answer records.
Authority
lublin.pl. 86400 SOA ns1.lublin.pl. dns.man.lublin.pl. 2013038287 14400 7200 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0