Office 365 is continuing to defer inbound mail from our systems, primarily from systems within our European infrastructure. We encourage customers to whitelist our IP addresses within Office 365, although that is appearing to help but not to fully solve the problem. We received conflicting information about the cause of the deferrals and are waiting on a response from higher level technicians at Office 365, but our assessment is that Microsoft may have implemented some new edge-based checks that are not helped by the whitelisting.
We are contacting Microsoft through several different channels, and are continuing to press for a solution on this matter. We would suggest that affected customers should not hesitate to also contact Microsoft support, as the additional pressure may help to achieve full resolution on this sooner.
We will post further updates as soon as more information becomes available.