masterdns.np6.net has no MX records.
Question and response
Question
dig masterdns.np6.net. MX
Answer
The response has no answer records.
Authority
np6.net. 3600 SOA level.np6.com. masterdns.np6.com. 2001100613 21600 3600 1209600 86400
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0