mail.tmknet.com.br has no CNAME records.
Question and response
Question
dig mail.tmknet.com.br. NS
Answer
The response has no answer records.
Authority
tmknet.com.br. 285 SOA ns1.tmknet.com.br. root.tmknet.com.br. 2505150944 10800 3600 7200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0