Outlook unable to connect to Exchange 2010


Recently, I was doing a simple Exchange migration from Exchange 2007 to Exchange 2010.  Once I moved all the mailboxes to the new exchange server, we noticed issues with Outlook.  The version of Outlook was 2003.

These were the issues being reported:

  • Random Outlook freezing and locking
  • Error – “Your Exchange Server administrator has blocked the version of Outlook that you are using. Contact your administrator for assistance.”
  • Error – “Cannot start Microsoft Office Outlook. Unable to open the Outlook window. The set of folders could not be opened.”
  • Error – “The connection to the Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action.”

So, I decided to check all the normal things for Exchange 2010 and Outlook 2003 compatibility:

  • A Public Folder database exists and is online
  • RPC Encryption disabled
  • Outlook 2003 is on latest Service Pack
  • Exchange is on latest Service Pack
  • EnablePushNotifications registry entry is set to “1”
  • Exchange was not restricting any Outlook versions. (How to check and Restrict)

Everything seemed OK.  I noticed during the migration that a proper Exchange 2003 to Exchange 2007 migration did not take place, and that in Active Directory, Old Exchange 2003 servers were present. I used ADSIedit to remove the decommissioned Exchange 2003 servers.  This also did not solve the problem, however.

Finally, the answer was a rather simple one:  The default public folder database for the Mailbox database was pointed to a decommissioned Exchange 2003 server’s database.  After Changing it to the Exchange 2010 Public Folder database – Outlook 2003 started behaving normally.


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