use.castellnet.com has no MX records.
Question and response
Question
dig use.castellnet.com. MX
Answer
The response has no answer records.
Authority
castellnet.com. 3600 SOA dns.castellnet.com. hostmaster.castellnet.com. 1192816079 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0