mx.zzzz.pro has no CNAME records.
Question and response
Question
dig mx.zzzz.pro. NS
Answer
The response has no answer records.
Authority
zzzz.pro. 4215 SOA ns1.he.net. hostmaster.he.net. 2026012715 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0