router.interplus.com.pl has no MX records.
Question and response
Question
dig router.interplus.com.pl. MX
Answer
The response has no answer records.
Authority
interplus.com.pl. 600 SOA ns1.itservice4u.pl. lukasz.itservice4u.pl.interplus.com.pl. 2026011502 86400 10800 3600000 10800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0