mx4.eftel.com has no CNAME records.
Question and response
Question
dig mx4.eftel.com. NS
Answer
The response has no answer records.
Authority
eftel.com. 4224 SOA dnsmaster.eftel.com. dnsmaster.eftel.com. 2023072801 10800 3600 864000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0