mx.uol.com.br has no MX records.
Question and response
Question
dig mx.uol.com.br. MX
Answer
The response has no answer records.
Authority
uol.com.br. 60 SOA a10-dns-uolcsfe1.host.intranet. root.uol.com.br. 2016057278 7200 3600 432000 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0