Issues delivering to Microsoft
Email delivery delays involving Microsoft 365
Status: Recovering — mail delivery to Microsoft restored
Updated: 4 September 2026, 14:55 CEST
Delivery to Microsoft 365 is returning to normal. Our platform is now handing mail off to Microsoft as expected, and we can see the effect of Microsoft’s mitigation. Remaining queued messages are being delivered.
Microsoft incident EX1467029 remains open on Microsoft’s side as a service degradation, with a further Microsoft update expected by 16:30 CEST.
Latest update
Microsoft identified that enforcement of a specific anti-spam model was throttling a subset of email traffic to and from Exchange Online. Microsoft is adding affected sending IP addresses to an allow list and disabling the model that caused the impact.
As of 14:26 CEST, Microsoft reported that telemetry showed a decrease in matching and throttling actions as the change propagated.
We can now confirm the same on our side:
- our platform is actively delivering mail to Microsoft
- we are seeing the effect of Microsoft’s fix
- mail is being handed off to Microsoft as expected
Messages that were previously deferred are being released from our queues. There is no indication of permanent mail loss.
Impact on our customers
- New email to and from Microsoft-hosted mailboxes is being delivered as expected.
- Some earlier messages may still arrive with a delay while remaining queues are cleared.
- Other mail routes that do not involve Microsoft-hosted mailboxes were not affected.
Microsoft incident details
| Field | Details | |---|---| | Title | Users may experience delays sending and receiving email messages from external domains in Exchange Online | | Issue ID | EX1467029 | | Affected service | Exchange Online | | Issue type | Incident | | Microsoft status | Service degradation (mitigation in progress) | | Start time | 4 September 2026, 12:19 CEST (GMT+2) | | User impact | Delays sending and receiving email messages from external domains in Exchange Online. Intermittent “Server busy” errors may affect multiple mailboxes. | | Cause | Enforcement of a specific anti-spam model, causing matching and throttling of a subset of email traffic | | Mitigation | Affected IPs added to an allow list; the contributing anti-spam model is being disabled |
Timeline
- 4 September 2026, 12:19 CEST — Microsoft reports the start of incident EX1467029.
- 4 September 2026, 12:21 CEST — Microsoft begins investigating a potential issue.
- 4 September 2026, 12:36 CEST — Microsoft reviews telemetry to isolate the source of the issue.
- 4 September 2026, 13:03 CEST — Initial finding: anti-spam protections may be contributing to impact for a subset of users.
- 4 September 2026, 13:59 CEST — Confirmed cause: enforcement of a specific anti-spam model. Microsoft begins allow-listing affected IPs and works to disable the model.
- 4 September 2026, 14:26 CEST — Microsoft reports that disablement is progressing and that throttling is decreasing as the change propagates. Rollout estimated to complete within 30 minutes.
- 4 September 2026, 14:55 CEST — Our platform is delivering mail to Microsoft again. We see the effect of Microsoft’s mitigation and can now hand off messages as expected. Remaining queued mail is being processed.
What we are doing
- Delivering previously queued messages to Microsoft.
- Monitoring inbound and outbound queues for Microsoft destinations.
- Tracking Microsoft incident EX1467029 until Microsoft closes the case.
- Updating this page after Microsoft’s next status update, or when we confirm that all remaining queues are clear.
What you can do
No action is required. If a specific message sent during the incident window has still not arrived after a further delay, contact our support team with the sender address, recipient address, approximate send time.
Reference: Microsoft 365 Service Health, issue EX1467029.
Next Microsoft update expected by 16:30 CEST.