ext.oss.as9143.net has no MX records.
Question and response
Question
dig ext.oss.as9143.net. MX
Answer
The response has no answer records.
Authority
ext.oss.as9143.net. 900 SOA ns1.as9143.net. dnsadmin.as9143.net. 113 10800 3600 2419200 900
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0