The email system was originally built on trust. Your mail server could claim to be sending on behalf of any domain it liked and the other server would trust it. Since spammers have been abusing that trust, some strategies were put in place to prevent the abuse.
SPF is a standard designed to allow the MCHS to prevent anyone in the world from sending email pretending to be from
mchs.org.au. The way it works is that they publish a DNS record under their domain that lists all the valid mail server IP addresses that are allowed to send email claiming to be from
The DNS record can also state what should be done with emails that come from other IP addresses. Unfortunately, in the case of
mchs.org.au they say that mail servers can "do what you like, we don't care".
The last part of their SPF record should read
-all instead of
?all. If it did, this mail may have been dropped instead of being delivered to your inbox.
Note: It also may not have been dropped depending on the Envelope-from address and the IP address the email was actually sent from.
DKIM is another standard designed to prevent malicious people from sending email pretending to be you. It works in a different way by cryptographically signing certain header fields using a private key and publishing the public key using DNS.
It's difficult to determine whether a domain uses DKIM or not without seeing the DKIM header in one of the emails from that domain.
They do publish a DKIM public key in their DNS. I guessed until I hit on the selector
default. If there is a DKIM header in the email (and the signature is validated) or a Received-From: header that contains either
18.104.22.168 then you can be certain that the email was actually sent from an MCHS server.