An email from this sender could not be delivered to your mailbox as it has failed DKIM verification. To comply with government security standards the ATO cannot accept emails that fail DKIM integrity checks because the email cannot be verified as genuine.

Currently there is an issue causing emails from organisations using Office 365 to fail DKIM verification.

Office 365 has implemented its own DKIM features and customers must ensure that outbound DKIM is correctly configured for their domain (DNS) and namespace (Office 356 Administration).

Resolution

How to enable DKIM on 365

You will need to enable DKIM outbound DNS Verification on either 365 

selector1._domainkey.domain.com
selector2._domainkey.domain.com

These need to point to 

selector1-domain-com._domainkey.onmicrosoftalias.onmicrosoft.com
selector2-domain-com._domainkey.onmicrosoftalias.onmicrosoft.com

Your onmicrosoftalias is the domain GUID and can be retrieved from the MX record for your domain

You then need to enable

View Powershell :  

New-DkimSigningConfig –DomainName domain.com –Enabled $true

Or through GUI : 

If you send out via another provider e.g. a spam filter you will need to check the method on the spam filter of enabling this