mail.gotheborg.com has no CNAME records.
Question and response
Question
dig mail.gotheborg.com. NS
Answer
The response has no answer records.
Authority
gotheborg.com. 461 SOA ns.aname.net. hostmaster.gotheborg.com. 1734953993 10800 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0