Thanks @FateCandylaneT , unfortunately we do not have such control over the mail severs as these are Microsoft 365 servers, we do not operate our own mail servers, I don't think many people do that, particularly in this segment of customers.

So all we have is the SFP record on the DNS we can set, it works absolutely fine for all other mail services such as MailChimp, SendGrid etc.

Your list of servers is a lot longer than the 5 servers when you look at the include:e.notification.intuit.com

Do you have a full list of all your mail server IP addresses so we can add them to the SPF record and hope the issue will be resolved.

Thanks

Paul