mail.gunnarhofmann.de has no CNAME records.
Question and response
Question
dig mail.gunnarhofmann.de. NS
Answer
The response has no answer records.
Authority
gunnarhofmann.de. 4510 SOA ns.gunnarhofmann.de. hostmaster.gunnarhofmann.de. 23 86400 28800 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0