mx.gplhost.com has no MX records.
Question and response
Question
dig wildduck.tusker.net.au. MX
Answer
The response has no answer records.
Authority
tusker.net.au. 1800 SOA gemma.ns.cloudflare.com. dns.cloudflare.com. 2395603200 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0