smtp20.acens.net has no MX records.
Question and response
Question
dig smtp20.acens.net. MX
Answer
The response has no answer records.
Authority
acens.net. 7200 SOA ns1.acens.net. hostmaster.acens.net. 1772130298 14400 3600 604800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0