mail.nexnet.de has no CNAME records.
Question and response
Question
dig mail.nexnet.de. NS
Answer
The response has no answer records.
Authority
nexnet.de. 10800 SOA pdns02.domaincontrol.com. administratoren-websites.nexnet.de. 2026022101 10800 3600 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0