mail.tnnet.fi has no CNAME records.
Question and response
Question
dig mail.tnnet.fi. NS
Answer
The response has no answer records.
Authority
tnnet.fi. 300 SOA timantti.tnnet.fi. admin.tnnet.fi. 2026030501 300 600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0