Symptoms
In a Microsoft Exchange Server 2013 environment, Exchange servers may experience the high CPU usage issue and the IIS worker process (w3wp.exe) consumes lots of CPU utilization, which is the MSExchangeMapiMailboxAppPool application pool. As a result, either you cannot connect to the Exchange Server 2013 servers or the Outlook client freezes.
Cause
This issue occurs because MSExchangeMapiMailboxAppPool is waiting for a global lock inside of system timer queue.
Resolution
To fix this issue, install Cumulative Update 19 for Exchange Server 2013 or a later cumulative update for Exchange Server 2013.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.
