mx.uhserver.com has no CNAME records.
Question and response
Question
dig mx.uhserver.com. NS
Answer
The response has no answer records.
Authority
uhserver.com. 59 SOA ns1.host.uol.com.br. admin.uolhost.com.br. 2025093001 43200 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0