mail.astra-dev.online has no CNAME records.
Question and response
Question
dig mail.astra-dev.online. NS
Answer
The response has no answer records.
Authority
astra-dev.online. 1443 SOA ganz.ns.cloudflare.com. dns.cloudflare.com. 2396599602 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0