mx3.eftel.com has no CNAME records.
Question and response
Question
dig mx3.eftel.com. NS
Answer
The response has no answer records.
Authority
eftel.com. 5153 SOA dnsmaster.eftel.com. dnsmaster.eftel.com. 2023072801 10800 3600 864000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0