Different versions of Outlook clients combined with different versions of Exchange Server may require close attention to configurations of both Exchange server and the Outlook client to achieve expected results. The following article helps understand these differences.
As Microsoft advances their Exchange infrastructure they are attempting to move away from the Public Folder concept from within the Exchange server.
In this attempt they have devised different means to access Free / Busy information. The information described in this article is for informational purposes only.
With Outlook 2003 and Exchange 2003, the client asked directly the information store to get free/busy information, which was stored in a system public folder.
Microsoft then changed its technology. Exchange 2007 and Exchange 2010 provide free/busy information through a web service. The client contacts the web service; the web service accesses the mailboxes for retrieving free/busy information. So the public folder is not used any more for this.
Note: If we speak about Exchange 2010 we address only Exchange 2010 SP1 in this article.
Outlook 2003 only can retrieve Free/Busy information by accessing the system public folder hosting this information. If you use this version as your messaging client and if you have Exchange 2007 or Exchange 2010 SP1 as server version you only have to install a public folder database.
Because Exchange 2007 and Exchange 2010 SP1 by default require an encrypted communication between MAPI client and server, you have to configure Exchange servers not to require encryption. This is done by a cmdlet on each Exchange 2010 SP1 server.
"Set-RpcClientAccess -Server Exchange_server_name -EncryptionRequired$False "
You can also retain the default encryption at server side and configure all Outlook 2003 clients to use encryption. This could be automated by Group Policies.
Outlook 2007 by default tries to get free/busy information by accessing a web service (through the availability service).
In an Exchange 2003 environment there is no web service present and Outlook 2007 accesses Public Folders without further configuration.
In an Exchange 2007 or Exchange 2010 environment you must force the messaging client to get the free/busy information from public folder. This is done by setting a registry key on the machines with Outlook 2007:
DWORD registry Key "UseLegacyFB"
You can distribute this registry key by GPO.
Instead of changing the client's configuration you might prefer a server solution. This solution works in Exchange 2007 and Exchange 2010 SP1 environments (Exchange 2010 without SP is not recommended for this).
The PowerShell cmdlet "Add-AvailabilityAddressSpace" forces the Availability Web Service to access public folders to retrieve free/busy information.
So the Outlook 2007 client connects to the availability server which then accesses the public folder database.
The cmdlet must be run for every domain you have imported objects from. For example, you have the SMTP domain "us.com" in your us.com-organization, you have to run this command:
Add-AvailabilityAddressSpace -ForestName partner.com -AccessMethod PublicFolder
After doing so, please restart Internet Information Server by running the iisreset command.
Result: all Outlook 2007 clients can get the free/busy information, which have been replicated by GALsync to your organization.
Outlook 2010 gets free/busy information by accessing a web service (availability service). . The regkey UseLegacyFB that you could use with Outlook 2007 is ignored by Outlook 2010, so you cannot connect to public folder to retrieve free/busy by this way. Outlook 2010 will only look to the mailbox for Free /Busy information.