co.nz has no MX records.
Question and response
Question
dig co.nz. MX
Answer
The response has no answer records.
Authority
co.nz. 3600 SOA loopback.dns.net.nz. soa.nzrs.net.nz. 2602281301 900 300 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0