smtprelay.aureon.com has no MX records.
Question and response
Question
dig smtprelay.aureon.com. MX
Answer
The response has no answer records.
Authority
aureon.com. 3600 SOA ns3k.aureon.com. hostmaster.netins.net. 2017103601 1800 3000 604800 86400
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0