Intermittent bounced emails inbound to M365 domains

Mailprotector is aware of intermittent bounces of inbound emails to Microsoft 365 domains. The bounces reference one of two reasons: "banned sending IP" or "blocked using Spamhaus." In both cases, Microsoft and Spamhaus do not indicate that the IP addresses are blocked when a delist request is made. Mailprotector has two open and active support requests with Microsoft to explain and resolve the situation. Mailprotector has been attempting to resolve the issue with Microsoft for over a week. Unfortunately, we have seen increased bounces in the last 24 hours. Partners and users may click on the delist links in the bounce notification. However, the delist will reply that the IP addresses are not listed. It is important to note that this is not an outbound reputation issue. Microsoft is randomly rejecting emails from IP addresses that only relay inbound emails after being filtered. The IP addresses are added to the recommended inbound connector for M365 deployments.