zabbix.maxnet.org.pl has no MX records.
Question and response
Question
dig zabbix.maxnet.org.pl. MX
Answer
The response has no answer records.
Authority
maxnet.org.pl. 3600 SOA dns1.maxnet.org.pl. red.maxnet.org.pl. 2025112500 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0