mail.42one.com has no CNAME records.
Question and response
Question
dig mail.42one.com. NS
Answer
The response has no answer records.
Authority
42one.com. 4800 SOA ns01.v-dns.de. hostmaster.v-dns.de. 2026022601 7200 3600 4800 4800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0