Summary: During this incident some customers hosted in the US region observed latency/slowness of outbound message delivery. For the impacted customers, a portion of messages were sent later than intended (up to 1.5 hours late). Delay events were not logged for the affected messages (contrary to the original report) because they were not attempted for delivery during the incident.
Incident Period: Jan 28 2019 from approximately 3:45 PM to 5:15 PM EST
Root Cause & Corrective Actions: The root cause was an availability issue of an underlying component used for suppression checks. We have identified several corrective actions: we made immediate improvements to the caching tier and over the next several weeks we’ll move to a more robust solution for storing suppression data.