However, when adding our accounts to Outlook, Outlook will set the incoming/outgoing mail server to melvilletennis.com.au or mail.melvilletennis.com.au
Note: I’ve checked and both 587 and 993 listeners at ax.email are open
On the other hand - have you already contacted the support team from your hosting platform (which seems to be VentraIP as maybe they would like to provide you other recommendations)?
PS: IMHO the CNAME setup suffer from the problem that the SSL cert configured on ax.email do not include autodiscover. into the Certificate Subject Alternative Name extension, thus the HTTPS connection will not be trusted (and most probably deferred by the mail client).
But here, on this public forum, we (from Axigen) or other community members (not necessarily affiliated with Axigen) are trying to answer / provide help when possible.