mx6.telemach.net has no CNAME records.
Question and response
Question
dig mx6.telemach.net. NS
Answer
The response has no answer records.
Authority
telemach.net. 5598 SOA ns.telemach.net. hostmaster.telemach.net. 2020092905 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0