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.
This issue occurs because MSExchangeMapiMailboxAppPool is waiting for a global lock inside of system timer queue.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.