Microsoft has posted a detailed update on its service status blog where it has explain the cause of the long downtime of Outlook.com and Exchange ActiveSync for many years earlier in the week. Microsoft has also claimed that the service is fully restored but there are still reports that there are issues with the service.
Microsoft has explained in the blog post that its system administrators identified the cause of the problem being “a failure in a caching service that interfaces with devices using Exchange ActiveSync.” This led to a cascading effect which flooded microsoft’s servers with the kind of traffic which its servers could not handle and crashed. In order to fix this problem, Microsoft had to take its Exchange ActiveSync down. Microsoft also need to change some hardware to ensure that the problem did not arise again. Microsoft has said:
This incident was a result of a failure in a caching service that interfaces with devices using Exchange ActiveSync, including most smart phones. The failure caused these devices to receive an error and continuously try to connect to our service. This resulted in a flood of traffic that our services did not handle properly, with the effect that some customers were unable to access their Outlook.com email and unable to share their SkyDrive files via email.
Microsoft has further said: “we apologize for letting … customers down this week.” The outage lasted for three days starting 14th August. The web access of outlook.com was restored the same day but the backlog of ActiveSync took more days, even until today the backlog is not fully clear.