mail2b.nrw.net has no CNAME records.
Question and response
Question
dig mail2b.nrw.net. NS
Answer
The response has no answer records.
Authority
nrw.net. 300 SOA a.ns.nrw.net. hostmaster.joker.com. 2026030235 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0