Hi Kelvin, The availability service is used for Outlook 2007 or higher version to retrieve free/busy information, for instance, Out of Offce status, free/busy in calendar schedule. see http://technet.microsoft.com/en-us/library/bb232134.aspx So, if you have Outlook 2007, I don't recommended you apply this change. Fiona Liao TechNet Community Support

Hi, I have a few Exchange 2010 SP1 RU6 mailbox role server, 2 of them are public folders server. All Outlook clients are unable to access Public Folders. This KB, http://support.microsoft.com/kb/2535105, seems related to my issue. I intend to fix it via registry key as follow. disable the Availability service: Click Start, click Run, type regedit in the Open box, and then click OK. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeRPC\ On the Edit menu, point to New, and then click Key.Type ParametersSystem, and then press Enter.Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeRPC\ParametersSystem On the Edit menu, point to New, and then click Dword Value.Type DisableAvailabilityServiceCalls, and then press Enter.In the details pane, right-click DisableAvailabilityServiceCalls, and then click Modify.In the Value data box, type 1, and then click OK. Exit Registry Editor. Question, 1. Should I apply the registry settings to only 2 public folders server or all the mailbox role servers? 2. Do I need to reboot the server after this registry key? 3. What is the purpose of availability service? Kelvin Teang

Hi Fiona, In this case, should I apply method 1 that mentioned from http://support.microsoft.com/kb/2535105 in order to fix access public folder issue? Please advise. Many thanks.Kelvin Teang

Hi Kelvin, Sorry for the delay response. May I know what isue are you encountering? Fiona Liao TechNet Community Support

Hi Fiona, I have multiple mailbox servers which 2 of them are hosting Public Folder. Users are unable to access Public Folder after a period of time. OWA no issue. There is a hotfix, http://support.microsoft.com/kb/2497453, for mailbox roles that hosting Public Folder.Kelvin Teang