Hi, I'm currently transitioning form Exchange 2003 to Exchange 2007. For now I've installed Exchange 2007 but the mailboxes still reside on Exchange 2003. I will move mailboxes in batches from 2003 to 2007. In order for the users to be able to keep using Outlook Webaccess we have to use the Exchange 2007 webaccess. As I understand we have to use the url https:<exchange 2007 server>/exchange in order to access Exchange 2003 mailboxes. However, when I use that url I get the following error: HTTP/1.1 501 Not Implemented https://<exchange 2007 server>/owa works, but then I get a message that the mailbox doesn't reside on the exchange 2007 server, which is correct of course. So what am I doing wrong, why can't I access exchange 2003 maibloxes from Web Access running on Exchange 2007? Franc.

hey, did you ever get a resolution to this? I'm having the same issue...

Hi, no untfortunately not. I ended up in moving all mailboxes at once. Franc.

I suspect an issue with the CAS configuration, this is a supported deployment scenario.Some information is available here: http://msexchangeteam.com/archive/2007/09/04/446918.aspx