mail.idc.net.pl has no MX records.
Question and response
Question
dig mail.idc.net.pl. MX
Answer
The response has no answer records.
Authority
idc.net.pl. 10800 SOA ns1.idc.net.pl. admin.idc.net.pl. 2025043000 10800 900 1209600 86400
Additional
. 0 OPT ; payload 2048, xrcode 0, version 0, flags 0