mail.gymmaster.com has no CNAME records.
Question and response
Question
dig mail.gymmaster.com. NS
Answer
The response has no answer records.
Authority
gymmaster.com. 2400 SOA gns21.cloudns.net. ns.treshna.com. 2026022702 12000 1800 1209600 2400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0