mx.klenk.at has no CNAME records.
Question and response
Question
dig mx.klenk.at. NS
Answer
The response has no answer records.
Authority
klenk.at. 2465 SOA dns1.a1.net. domainadmin.a1.net. 2025050600 10800 3600 1814400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0