mail.atomicvps.com has no CNAME records.
Question and response
Question
dig mail.atomicvps.com. NS
Answer
The response has no answer records.
Authority
atomicvps.com. 10794 SOA ns.hostnexus.com. lflynn.hostnexus.com. 2021042601 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0