cdxmailin02.datev.com has no CNAME records.
Question and response
Question
dig cdxmailin02.datev.com. NS
Answer
The response has no answer records.
Authority
datev.com. 600 SOA ns01.datev.de. dnsmaster.datev.de. 2602251239 21600 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0