This isn’t an error from Netlify. This reads like the default error message on an Apache server. Does this happen on multiple devices or just one?
apexbuildingandmanagement.com.au is using Netlify DNS and appears correctly configured.
A DKIM is a TXT record.
While there are both SPF and TXT the SPF record type is rarely used and SPF records use TXT instead. You can leave this TXT
$ dig apexbuildingandmanagement.com.au TXT
apexbuildingandmanagement.com.au. 4502 IN TXT "v=spf1 include:spf.protection.outlook.com -all"
and unless Microsoft 365 requires it, remove this SPF
$ dig apexbuildingandmanagement.com.au SPF
apexbuildingandmanagement.com.au. 4502 IN SPF "v=spf1 include:spf.protection.outlook.com -all"
And I can see the MX record
$ dig apexbuildingandmanagement.com.au MX
apexbuildingandmanagement.com.au. 4502 IN MX 0 apexbuildingandmanagement-com-au.mail.protection.outlook.com.
Propagation does take time read: [Support Guide] Why do DNS / SSL changes take up to 48 hours to propagate? (TTL)