We are in the process of upgrading from Exchange 2003 to Exchange 2010. We've moved a couple of mailboxes to the the new server, including mine. In Outlook 2007, I can view additional mailboxes. However if one of those mailboxes have been moved to Exchange 2010 I get an error message that the folder cannot be expanded. If the mailbox is still on the Exchnage 2003 server, I am able to view it in Outlook. How do I fix this? There are other employess that have access to additional mailboxes so I'd like to get this taken care of before we start moving everyone's mailboxes to the new Exchange 2010 server. Thanks for any assistance you can provide with this.