mail.cm.sonera.com has no CNAME records.
Question and response
Question
dig mail.cm.sonera.com. NS
Answer
The response has no answer records.
Authority
sonera.com. 8401 SOA namesurfer.inet.fi. hostmaster.telia.fi. 2026021312 28800 7200 3456000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0