mail2.servicioatt.com.mx has no CNAME records.
Question and response
Question
dig mail2.servicioatt.com.mx. NS
Answer
The response has no answer records.
Authority
servicioatt.com.mx. 2998 SOA dns.alestra.net.mx. soporteip.axtel.com.mx. 762215068 10800 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0