KB Article: http://support.microsoft.com/kb/2535105
Microsoft Outlook client applications experience connectivity issues when many Microsoft Exchange RPC Client Access service threads on a public folder are waiting for responses from the Availability service. For example, this issue occurs when there are more than 500 threads waiting for responses on a public folder.
- There is no option to disable the Availability service on an Exchange Server 2010 Service Pack (SP1) server.
- If you restart the Exchange RPC Client Access service on the Exchange Server 2010 SP1 public folder server, this issue is temporarily resolved.