mx20.positive-internet.com has no CNAME records.
Question and response
Question
dig mx20.positive-internet.com. NS
Answer
The response has no answer records.
Authority
positive-internet.com. 3340 SOA dns0.positive-internet.com. hostmaster.positive-internet.com. 2025111601 3600 1800 1814400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0