mail.forestera.se has no CNAME records.
Question and response
Question
dig mail.forestera.se. NS
Answer
The response has no answer records.
Authority
forestera.se. 4851 SOA ns1.netnames.net. hostmaster.cscdns.net. 2018081903 10800 1800 3600000 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0