Www3.pubnix.net has no MX records.
Question and response
Question
dig Www3.pubnix.net. MX
Answer
The response has no answer records.
Authority
pubnix.net. 86400 SOA ns1.pubnix.net. root.pubnix.net. 2025085136 3600 900 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0