mail.develooper.com has no CNAME records.
Question and response
Question
dig mail.develooper.com. NS
Answer
The response has no answer records.
Authority
develooper.com. 321 SOA ns.develooper.com. dnsoper.bitnames.com. 2026021981 600 600 4838400 360
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0