ns4.stratoserver.net has no MX records.
Question and response
Question
dig ns4.stratoserver.net. MX
Answer
The response has no answer records.
Authority
stratoserver.net. 1800 SOA ns.stratoserver.net. hostmaster.stratoserver.net. 2020129553 10000 14400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0