mx4.cobytes.email has no CNAME records.
Question and response
Question
dig mx4.cobytes.email. NS
Answer
The response has no answer records.
Authority
cobytes.email. 297 SOA ns1.cobytes.io. hostmaster.cobytes.io. 2026011500 14400 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0