Certain Microsoft Outlook client applications experience connectivity issues when many Microsoft Exchange RPC Client Access service threads that are on a public folder are waiting for responses from the Availability service. For example, this problem occurs when more than 500 threads wait for responses on a public folder.
No option exists to disable the Availability service on a server that is running Exchange Server 2010 Service Pack (SP1).
If you restart the Exchange RPC Client Access service on the Exchange Server 2010 SP1 public folder server, this problem is temporarily resolved.
This problem occurs because of a new feature in Exchange Server 2010 SP1. This new feature uses the Microsoft Exchange RPC Client Access service as a proxy for earlier versions of the Availability service (free/busy information). Therefore, if you have a public folder that is installed on an Exchange Server 2010 SP1 server, the Microsoft Exchange RPC Client Access service intercepts the free/busy information requests.
To resolve this problem, use one of the following methods.
Upgrade all clients to Outlook 2007 or a later version which uses Exchange Web Services (EWS) to make availability service calls directly to the Exchange Client Access server.
Install the following update on the Exchange Server 2010 SP1 mailbox servers hosting a public folder database:
2497453 FIX: Application may stop responding after several HTTP requests are aborted if you use the HttpWebRequest class to send requests in the .NET Framework
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
Caution The following issues may occur if you apply this method:
In an Office 365 and on-premises Exchange Server hybrid deployment, or in the federated organizations, legacy clients such as Microsoft Office Outlook 2007 or Microsoft Office Outlook 2003 will no longer receive free/busy data from the cloud site or from the remote organization.
The most current free/busy data will not be reported for legacy clients. The data could be up to 15 minutes out-of-date.
To resolve this problem, follow these steps on the mailbox server hosting a public folder database:
Click the following article number to go to the article in the Microsoft Knowledge Base, and then install the update rollup that is described in the article:
2579150 Description of Update Rollup 4 for Exchange Server 2010 Service Pack 1
Disable the Availability service.
To have us disable the Availability service for you after you install Update Rollup 2579150, go to the "Fix it for me" section. If you prefer to disable the Availability service yourself, go to the "Let me fix it myself" section.
Fix it for me
To disable the Availability service automatically, click the Fix it button or link. Then, click Run in the File Download dialog box, and follow the steps in the Fix it wizard.
This wizard may be in English only. However, the automatic fix also works for other language versions of Windows.
If you are not on the computer that has the problem, save the Fix it solution to a flash drive or a CD, and then run it on the computer that has the problem.