server2.filtermail.eu has no CNAME records.
Question and response
Question
dig server2.filtermail.eu. NS
Answer
The response has no answer records.
Authority
filtermail.eu. 71733 SOA ns1.sqr.nl. hostmaster.filtermail.eu. 2025042201 3600 900 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0