Currently, I have a domain environment with two DC's/GC's (Server 2008 R2)and two Exchange Servers (Exchange 2003 on Server 2003,Exchange 2007 on Server 2008 R2). I am migrating all mailboxes from the Exchange 2003 to the 2007, but I am still a ways away from having that complete. My issue is this. I have some new users I created and they are getting a "The connection to microsoft exchange is unavailable" message when I try to create their accounts in Outlook 2007. None of the users I migrated from the old exchange server have this issue. Autodiscover is working normally as far as I can tell. I have a feeling this is a group policy problem but I can't be sure.
As a test, I installed Outlook 2010 on a computer and was able to get the new user's mailbox to connect. Unfortunately, upgrading to 2010 is not a solution because I would need to upgrade all my users to it, since many of them have roaming profiles and I don't want them getting on a machine with 2010, then logging onto a different machine with 2007.. I am sure that would cause problems..
I read somewhere that the issue could be related to the way exchange 2007 handles legacy mailboxes, but again, I'm not sure if that is related to this..
Any help is appreciated!