exchext.swm.de has no CNAME records.
Question and response
Question
dig exchext.swm.de. NS
Answer
The response has no answer records.
Authority
swm.de. 60 SOA ns.swm.de. firewalladm.swm.de. 2026022701 3600 7200 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0