extmail.bigpond.com has no MX records.
Question and response
Question
dig extmail.bigpond.com. MX
Answer
The response has no answer records.
Authority
extmail.bigpond.com. 500 SOA cladnsf5.bigpond.com. hostmaster.cladnsf5.bigpond.com. 2023050204 10800 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0