Symptoms
Assume that you configure public folder replication in a mixed Microsoft Exchange Server 2003 and Microsoft Exchange Server 2010 environment. When an Exchange Server 2010 user tries to view an Exchange Server 2003 user’s free/busy information, the user intermittently cannot view the free/busy information, or the user encounters a long delay when he or she tries to view the free/busy information.
Cause
This issue can occur if the Availability Service selects a remote public folder server to retrieve the free/busy information. If the remote public folder server is connected over a slow WAN link, the issue that is described in the "Symptoms" section can occur.
Note The Availability Service does not search for a local public folder replica before it selects a remote public folder server.
Resolution
To resolve this issue, install the following update rollup:
2645995 Description of Update Rollup 1 for Exchange Server 2010 Service Pack 2
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
More Information
After you install Update Rollup 1 for Exchange Server 2010 Service Pack 2, Exchange Server 2010 retrieves a list of all the public folder stores and determines the host server for each public folder store. From that list, Exchange Server 2010 computes the connection cost from the Client Access server (CAS) to the public folder server. Then, Exchange Server 2010 selects the public folder server that has the lowest connection cost.
After Exchange Server 2010 selects the public folder server, Exchange Server 2010 identifies all the folders that contain free/busy information. Then, Exchange Server 2010 performs the following actions:
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Retrieves the organizational unit (OU) information from the folder name
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Retrieves a replica list and sorts the replica list by connection cost
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Saves a mapping from each OU to the sorted replica list
When Exchange Server 2010 receives a request for free/busy information, Exchange Server 2010 establishes the free/busy OU information from the legacyExchangeDN attribute and uses the mapping table to route the request.
References
For more information about a similar issue, click the following article number to view the article in the Microsoft Knowledge Base:
971349 Exchange Server 2007 users intermittently cannot access an Exchange Server 2003 user's Free/Busy information in Office Outlook 2007 For more information about a similar issue, click the following article number to view the article in the Microsoft Knowledge Base:
947346 Exchange Server 2007 mailbox users cannot retrieve the free/busy information for Exchange Server 2003 mailbox users in a large Exchange Server organization that has more than 100 administrative groups For more information about how to configure public folder replication, visit the following Microsoft website:
General information about how to configure public folder replicationFor more information about public folder replication, visit the following Microsoft website:
