mail.ext.aetzer.de has no CNAME records.
Question and response
Question
dig mail.ext.aetzer.de. NS
Answer
The response has no answer records.
Authority
aetzer.de. 807 SOA ns.inwx.de. hostmaster.inwx.de. 2026022200 10800 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0