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.

Email delivery delays involving Microsoft 365

Status: Service degradation Updated: 4 September 2026, 12:50 CEST

We are seeing delays, and in some cases temporary delivery failures, for email sent to or received from mailboxes hosted on Microsoft 365 (Exchange Online). Other mail routes that do not involve Microsoft-hosted mailboxes are operating normally.

This is caused by an active Microsoft incident. Microsoft is investigating under issue ID EX1467029 and currently classifies the issue as a service degradation affecting Exchange Online.

Impact on our customers

• Inbound email to customers whose mailboxes are hosted at Microsoft may be delayed.
• Outbound email from our platform to external recipients on Microsoft 365 / Outlook.com may be delayed or temporarily deferred.
• Messages are being queued and retried. There is no indication of permanent mail loss at this time.
• Some delivery attempts may return intermittent “Server busy” errors from Microsoft.

Microsoft incident details

| Field | Details | |---|---| | Title | Users may experience delays receiving email messages from external domains in Exchange Online | | Issue ID | EX1467029 | | Affected service | Exchange Online | | Issue type | Incident | | Microsoft status | Service degradation | | Start time | 4 September 2026, 12:19 CEST (GMT+2) | | User impact | Delays receiving email messages from external domains in Exchange Online. Intermittent “Server busy” errors may affect multiple mailboxes. | | Scope | Users attempting to receive email from external domains in Exchange Online. Microsoft may update this scope as the investigation continues. |

Timeline

• 4 September 2026, 12:19 CEST — Microsoft reports the start of incident EX1467029.
• 4 September 2026, 12:36 CEST — Microsoft update: engineers are reviewing service monitoring telemetry to isolate the source of the issue and establish a fix. Next Microsoft update expected by 14:30 CEST.
• 4 September 2026, 12:50 CEST — We confirm impact on mail flow to and from Microsoft-hosted mailboxes. Independent providers are reporting the same symptom. We have notified Microsoft and are monitoring queues and retries.

What we are doing

• Monitoring inbound and outbound queues for Microsoft destinations.
• Retrying deferred messages automatically.
• Tracking Microsoft incident EX1467029 and related public reports.
• Updating this page when Microsoft publishes a new status or when delivery returns to normal.

What you can do

No action is required on your side. Please do not resend large volumes of the same messages, as this can increase queue time.

Reference: Microsoft 365 Service Health, issue EX1467029.
Restoration depends on Microsoft completing its remediation for Exchange Online.

We observed queues on our systems with messages getting delivered to Exchange online. The message is “Try again later” This normally indicates internet issues on the Microsoft side. We will keep monitor and update when we know more.