ip.interplus.com.pl has no MX records.
Question and response
Question
dig ip.interplus.com.pl. MX
Answer
The response has no answer records.
Authority
ip.interplus.com.pl. 3600 SOA dns1.interplus.com.pl. lukasz.itservice4u.pl. 2018110201 43200 900 1209600 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0