s0.sunmail.pl has no MX records.
Question and response
Question
dig s0.sunmail.pl. MX
Answer
The response has no answer records.
Authority
sunmail.pl. 3600 SOA dns.home.pl. admin.home.pl. 1651734928 14400 7200 2419200 3600
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0