mx20.013net.net has no CNAME records.
Question and response
Question
dig mx20.013net.net. NS
Answer
The response has no answer records.
Authority
013net.net. 4065 SOA dns.netvision.net.il. hostmaster.netvision.net.il. 2025090901 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0