smtpmx.axtel.com.mx has no NS records.
NS records for this zone are defined at axtel.com.mx.
NS records for this zone are defined at axtel.com.mx.
Question and response
Question
dig smtpmx.axtel.com.mx. NS
Answer
The response has no answer records.
Authority
axtel.com.mx. 3600 SOA ns-mty.axtel.net. soporteip.axtel.com.mx. 762215079 7200 1200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0