mx2.plnfilter.fi has no CNAME records.
Question and response
Question
dig mx2.plnfilter.fi. NS
Answer
The response has no answer records.
Authority
plnfilter.fi. 169 SOA ns1.planeetta.net. hostmaster.planeetta.net. 2023120500 7200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0