ns2.lstn.net has no MX records.
Question and response
Question
dig ns2.lstn.net. MX
Answer
The response has no answer records.
Authority
lstn.net. 2560 SOA ns1.limestonenetworks.com. noc.limestonenetworks.com. 1772017766 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0