Increased error rate communicating with Outlook.com calendars

Microsoft Issue ID EX1112414 remains open however a preliminary root cause has been provided:

"A recent service update to an authentication component is unintentionally preventing access for a subset of users, resulting in intermittent service unavailability."

We've seen no further issues since our previous update and error rates remain consistent with healthy operations so we're going to consider this incident resolved.

As of 16:30 UTC we're seeing service levels back at their expected levels and a drastic reduction in error rates.

Outlook.com profiles are now authenticating consistently.

Microsoft Issue ID EX1112414 remains open however and so we'll continue to monitor things for a while longer in the expectation that this issue is now resolved but just to be sure.

Error rates remain fairly consistent and Microsoft are in the process of rolling out a fix.

We've yet to see the effects of this, are continuing to monitor, and will advise of any further changes.

Error rates remain fairly consistent.

We're continuing to monitor and will advise of any further changes.

Error rates remain fairly consistent.

We're continuing to monitor and will advise of any further changes.

We've ascertained that the issue isn't down to changes on our side and are tracking live issue with Outlook.com.

Microsoft are reporting on this as Issue ID EX1112414.

We can see that not all profiles are affected and that, of those that are, retries do eventually succeed.

We'll continue to monitor and advise of any further changes.

We've identified that some Outlook.com profiles may be increased error rates when authenticating with Microsoft's APIs, causing sync failures for those affected. This appears to be related to an ongoing issue with Outlook.com

We're investigating the root cause and will update this incident as we understand more.