mail.domaku.com has no CNAME records.
Question and response
Question
dig mail.domaku.com. NS
Answer
The response has no answer records.
Authority
domaku.com. 1626 SOA ns1.nodoxy.com. hostmaster.domaku.com. 2026030501 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0