mail.itsecurity.de has no CNAME records.
Question and response
Question
dig mail.itsecurity.de. NS
Answer
The response has no answer records.
Authority
itsecurity.de. 222 SOA ns.itsecurity.de. hostmaster.itsecurity.de. 2026011708 14400 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0