mx01.arz.at has no CNAME records.
Question and response
Question
dig mx01.arz.at. NS
Answer
The response has no answer records.
Authority
arz.at. 60 SOA nsi.local. dns-admin.arz.at. 1197 10800 3600 1209600 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0