ActiveSync clients cannot connect or synchronizing is delayed in an Exchange Server environment

Applies to: Exchange Server 2016 Enterprise EditionExchange Server 2013 Enterprise

Symptoms


In a Microsoft Exchange Server 2016 or Microsoft Exchange Server 2013 environment, ActiveSync clients cannot connect or they experience delays when user synchronize their mobile device. This issue occurs after the ActiveSync application pool runs for some time, usually for several weeks. Additionally, you may experience the following behavior:

  • The ActiveSync application pool consumes lots of memory.
  • The .NET CLR Memory/% Time in GC counter for the w3wp instance that corresponds to the ActiveSync application pool is unusually high.
  • TCP port exhaustion occurs because of the high number of requests in ActiveSync.
  • The W3SVC_W3WP/Active Requests counter for the MSExchangeSyncAppPool instance shows a steadily increasing value over several days or weeks.
  • The netstat -anob command may show many connections in a CLOSE_WAIT state.

Cause


This is a known issue that occurs when ActiveSync Ping commands become stranded in the application pool.

Workaround


To work around this issue, periodically cycle the ActiveSync application pool to release the stranded commands.

For more information about how to configure an application pool to automatically recycle at regular intervals, see the "Recycling Settings for an Application Pool <recycling>" topic on the Microsoft Docs website.