mail.xenox.systems has no CNAME records.
Question and response
Question
dig mail.xenox.systems. NS
Answer
The response has no answer records.
Authority
xenox.systems. 5283 SOA ns1.xenox-systems.net. postmaster.xenox.systems. 2025050912 86400 10800 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0