mx.bol.com.br has no CNAME records.
Question and response
Question
dig mx.bol.com.br. NS
Answer
The response has no answer records.
Authority
bol.com.br. 452 SOA a10-dns-uolcsfe1.host.intranet. nsmaster.bol.com.br. 463 3600 1800 432000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0