Summary of impact: Between 00:00 - 05:30 UTC customers mail flow may have been delayed due to issues with the Exclaimer Cloud service.
Root cause: Preliminary investigation showed that our front-door proxy certificate that controls TLS connections between Office 365 and Exclaimer Cloud had expired.
Mitigation: Once our engineers had been made aware of the issue, an updated certificate was deployed to all regions between the hours of 04:00 - 05:30 UTC.
Next steps: We are currently investigating how this was not picked up by our SSL life-cycle management processes and more importantly, why our automated alert monitoring did not trigger our on-call NOC team at point of expiry.