mx6.macau.ctm.net has no MX records.
Question and response
Question
dig mx6.macau.ctm.net. MX
Answer
The response has no answer records.
Authority
macau.ctm.net. 3600 SOA vassun1.macau.ctm.net. helpdesk.macau.ctm.net. 2016073723 86400 7200 2419200 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0