mail.telia.net has no CNAME records.
Question and response
Question
dig mail.telia.net. NS
Answer
The response has no answer records.
Authority
telia.net. 1200 SOA dns1.telia.com. backbone.telia.net. 2026030300 10800 3600 604800 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0