mail.virtuaserver.com.br has no CNAME records.
Question and response
Question
dig mail.virtuaserver.com.br. NS
Answer
The response has no answer records.
Authority
virtuaserver.com.br. 10800 SOA ns.virtuaserver.com.br. root.virtuaserver.com.br. 1772572722 28800 7200 604800 39600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0