n8.cpa.net.pl has no MX records.
Question and response
Question
dig n8.cpa.net.pl. MX
Answer
The response has no answer records.
Authority
net.pl. 3600 SOA a-dns.pl. dnsmaster.nask.pl. 1772139304 900 300 2592000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0