Message from Microsoft:
EX75270 - E-Mail and calendar access - Service degradation
Service degradation - Aug 18, 2016 3:52 AM
Current Status: We're continuing to analyse data from the recent update to isolate the issue. We're also investigating potential interconnectivity issues within the Exchange subsystems.
User Impact: When using the Outlook desktop client in Online mode, messages may not appear to be correctly marked as read or unread until the user refreshes the current folder. While we're focused on remediation, users can switch between folders to see an updated list of read and unread items in Outlook. Messages will appear correctly in other clients such as Outlook on the web or mobile apps.
Scope of Impact: A few customers have reported this issue, and our analysis indicates that impact is specific to a subset of users who are served through the affected infrastructure.