bounce01.emaillabs.net.pl has no MX records.
Question and response
Question
dig bounce01.emaillabs.net.pl. MX
Answer
The response has no answer records.
Authority
emaillabs.net.pl. 1800 SOA athena.ns.cloudflare.com. dns.cloudflare.com. 2397511627 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0