ns2.tierra.net has no MX records.
Question and response
Question
dig ns2.tierra.net. MX
Answer
The response has no answer records.
Authority
tierra.net. 3600 SOA ns1.domaindiscover.com. hostmaster.tierra.net. 2026022303 7200 1800 604800 28800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0