Summary of Impact: Between 13:50 and 16:30 UTC customers may have experienced issues with queued messages in Exchange Online (EXO) due to Microsoft Issues.
Root Cause: Issues with Microsoft Office 365 meant that messages were not being delivered to Exclaimer in a timely manner. A small percentage of messages were not reaching our infrastructure and therefore they entered EXOs retry loop.
Mitigation: Microsoft resolved their service degradation. Once EXO could send us the message correctly, customers no longer experienced any issues.
Next Steps: We are working with Microsoft to understand why their service suffered this issue. We have made changes to our monitoring platform to help us alert customers faster if we see similar issues again.