12:30pm Pacific — Our monitoring has shown that the cluster at the German datacenter, which experienced high load yesterday morning Pacific time, has been stable for the last 24 hours.
Additionally, our engineering team has identified a likely contributor to this and the several other incidents of high load we have seen over the last several weeks. Specifically, the antivirus software that was added last quarter as a fourth malware detection engine within the Mail services, was responding sufficiently slowly under certain types of traffic as to create back pressure within the system. (Note that this is a different antivirus engine than the one being introduced for the Managed AV offering with the MAX RM service.) We are working with the antivirus vendor to attempt to replicate the issue under testing conditions, and to take appropriate steps to mitigate the risk of a similar issue.
We apologize for the inconvenience to customers that were affected by this.