Exclaimer incident
Delivery delays for messages sent from Outlook and Exchange
Exclaimer experienced a notice incident on September 22, 2026 affecting EU: Server-Side: Mail Routing - Office 365 and US: Server-Side: Mail Routing - Office 365 and 1 more component, lasting 16d 21h. The incident has been resolved; the full update timeline is below.
Affected components
Update timeline
- investigating Sep 22, 2026, 10:58 AM UTC
Exclaimer engineers are investigating a delivery delay affecting some messages sent from Outlook and Exchange to Exclaimer Cloud. Some of these messages may be retried by the sender and may appear as temporary deferrals rather than delivery failures. We are not currently aware of any confirmed message loss and will provide updates as we learn more.
- identified Sep 22, 2026, 03:19 PM UTC
Exclaimer has identified that a small subset of messages (~0.02%) are delayed when routed through Exclaimer due to a suspected issue within Microsoft's servers. This has been raised with Microsoft to investigate alongside Exclaimer Engineers. Sent messages will be received with a signature applied, as expected. If you are seeing issues with message deliverability, please reach out to our support team, who will be happy to assist.
- monitoring Sep 27, 2026, 07:33 PM UTC
Mail delivery has resumed as normal and our engineers are seeing significantly less errors. The team are awaiting confirmation of a fix implemented on Microsoft servers and will be monitoring until tomorrow morning to confirm.
- resolved Oct 09, 2026, 08:40 AM UTC
The original impact of the issue has been mitigated by Microsoft changes. Exclaimer Engineers are continuing to work together with Microsoft to establish a root cause. If you have any questions or concerns, please reach out to our great support team, who will be more than happy to help answer any questions.