mailz.sdu.dk has no CNAME records.
Question and response
Question
dig mailz.sdu.dk. NS
Answer
The response has no answer records.
Authority
sdu.dk. 884 SOA ns1.sdu.dk. dns.sdu.dk. 2012273876 86400 7200 2419200 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0