ao has no MX records.
Question and response
Question
dig ao. MX
Answer
The response has no answer records.
Authority
ao. 3600 SOA a.ns.ao. hostmaster.dns.ao. 1771716601 86400 7200 2592000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0