Intermittent bounced emails inbound to M365 domains

Bounces for "Banned Sending IP" and "Blocked using Spamhaus" have been all but absent for the last seven days.

Confirmation of resolution has not been received from Microsoft, but the current status of deliverability and information from Microsoft gives us reasonable confidence that this issue is on a path to resolution. We will continue monitoring email deliverability for this incident.

As a reminder, if there is a recurrence, Microsoft recommends that the sender follow the delisting instructions in the NDR (bounce notification) and resend the email.

Mailprotector has noticed an increase in the amount of emails with a “Banned Sending IP” bounce from M365 within the last 12 hours. This previously was resolved on May 1st, but the issue has returned.

This is still occurring in very small volumes, but we understand any bounce from the system is a disruption in business function. Due to this, we have reopened our case with Microsoft and are attempting to re-engage them.

We would recommend having the sender send the email again since it will go through the second time. It is important to note that this is not an outbound reputation issue.

Microsoft recommends that the sender follow the delisting instructions in the NDR (bounce notification) and resend the email. Mailprotector is attempting to work the problem with Microsoft to resolve the issue permanently.