mail.zbscloud.com has no CNAME records.
Question and response
Question
dig mail.zbscloud.com. NS
Answer
The response has no answer records.
Authority
zbscloud.com. 3599 SOA zbscloud.com. tech.zbscloud.com. 2026011301 3600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0