_netblock2.man.poznan.pl has no MX records.
Question and response
Question
dig _netblock2.man.poznan.pl. MX
Answer
The response has no answer records.
Authority
man.poznan.pl. 10800 SOA rose.man.poznan.pl. bind.man.poznan.pl. 2026030201 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0