mxrelay-ip-40.internet1.de has no CNAME records.
Question and response
Question
dig mxrelay-ip-40.internet1.de. NS
Answer
The response has no answer records.
Authority
internet1.de. 3468 SOA ns.internet1.de. hostmaster.centron.de. 2026030417 10000 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0