Thanks I have done a few more checks.

When I originally tested I used the same domain for the test email as the one we receive copies on. I have now tested sending to my personal gmail account and I received it with no problem but still no copy to the company domain.

I think the issue may be that because of the volume of spoofed emails sent purporting to be from the notification.intuit.com domain that domain is being blocked at a higher level on servers.

I have tried whitelisting the domain in the spam filters on our server but it still doesn't get through.

I also checked the domain for intuit for blacklisting on MX Toolbox but there doesn't seem to be any blacklisting of it so bit of a mystery why it should be happening.

The fact that it isn't blacklisted would indicate its an issue with the Intuit servers and this is something that they should be able to fix relatively quickly so I have no idea why they haven't dealt with it. I do wonder about the knowledge of their engineering team as it seems they have an inability to fix the most basic issues.