Exclaimer Outage History

Issue: Possible Routing issues within MEA & US region for Microsoft Customers Incident Length: ~70 hour\(s\) Incident Date: 4/4/2026, UTC 9:37– 8:07 7/4/2026 Incident Status: Investigating **Summary** Mail flow for customers in the Middle East and Africa \(MEA\) region would encounter issues routing messages to Exclaimer, with Exchange servers reporting that the exclaimer smtp hosts rejected or did not respond to the request. We are still awaiting a full Post Incident Review from Microsoft and will update this Postmortem with additional information once it is available. **Root Cause** The issue is believed to be a configuration issue within Exchange in the region, preventing the connection to Exclaimer servers within the UAE or US region. All impacted messages appear to have been deferred, resulting in them being delivered at a later time, further confirming the expected mail flow between Exclaimer and Exchange Online. **Mitigation** Some Exchange servers which were consistently noted to be failing to provide the email to Exclaimer relays when requested, were passed over to Microsoft for review. Shortly afterwards these instances stopped appearing to submit traffic to Exclaimer, suggesting they have been had been taken out of service. Exclaimer Engineers have internally made changes to how message logs are stored between our servers, helping to improve and identify potential issues and errors within the STARTTLS process

Issue: Messages failed to be routed through Exclaimer correctly within AU region Incident Length: 3 hour\(s\) and 6 minutes Incident Date: 01/04/2026 UTC 05:53– 8:59 Incident Status: Resolved **Summary** Australian Region customers with the Sent Items feature enabled would encounter an issue routing messages, resulting in message delivery issues and non-delivery reports \(NDRs\) being received. **Root Cause** The issue was caused by a recently enabled mail processing feature globally, which introduced unexpected behavior within the SMTP proxy servers. This affected how messages were handled when routing back to Exchange Online. **Mitigation** Initial resolution was implemented by reverting the mail processing feature update globally. Further improvements to error handling have since been implemented to identify the cause of similar issues faster in the future. **Incident Timeline** 01/04 5:53 – Incident is declared after customer reports of mail flow issues are received to the Support Team 5:57 – Initial investigation indicates the issue appears to be isolated to AU region customers. 6:03 – Exclaimer Engineers confirm the resulting error code correlates with error logs within internal logging 6:32 – Initial hypothesis suggests degradation with an external SMTP provider is the cause of the issue. Whilst they announce a fix, the backlog of impacted messages does not change. 6:41 – Error rates begin to decrease and incident is believe to be resolved. 7:08 – Exclaimer Engineers monitoring note that a drop in 5xx errors is visible, along with a drop in active message counts. Suggesting correlation between the errors being seen and the number of messages submitted to Exclaimer. 7:32 – Engineers begin investigating internal systems further for any lingering issues. 7:37 – The error is confirmed to be related to routing the email back to Exchange Online, disproving the earlier hypothesis. Recent changes to mail routing are reverted to monitor for impact or changes. The error rate is noted to instantly drop at this time. 8:03 – The error rate begins to approach zero, investigation into the cause within recent releases begins. As part of this incident, areas of improvement within internal and external communication have been identified. Action has been taken to improve this and prevent future instances of misattribution and miscommunication from occurring.