I'm in the process of an 03 to 2010 migration.. When I log into 2010 OWA with an 03 mailbox it prompts me to log in again (it does redirect to legacy url) and when I do it gives me an error on the page..
Paul Cunningham's blog said the fix was to enable forms based authentication on the 2003 server (Servers > Server > Protocols > HTTP > Exchange Virtual Server > right click > settings > click..)..
Doing this did indeed fix legacy redirect.. When I would log into 2010 OWA as an 03 user I was instantly redirected right into 03 OWA..
However, ActiveSync on mobile broke.. The following was logged. If anyone could help it'd be greatly appreciated.
Thanks
Event Type: Error Event Source: Server ActiveSync Event Category: None Event ID: 3031 Date: 7/16/2013 Time: 10:46:43 AM User: domain\jsmith Computer: SERVER Description: The mailbox server [SERVER.DOMAIN.com] does not allow "Negotiate" authentication to its [exchange] virtual directory. Exchange ActiveSync can only access the server using this authentication scheme. For information about how to configure Exchange virtual directory settings, see Microsoft Knowledge Base article 817379, "Exchange ActiveSync and Outlook Mobile Access errors occur when SSL or forms-based authentication is required for Exchange Server 2003" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=817379). For information about how to properly configure IIS to support Kerberos and NTLM authentication, see Microsoft Knowledge Base article 215383, "How To Configure IIS to Support Both Kerberos and NTLM Authentication" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=215383). This issue may occur after installing Windows SharePoint Services on a server running Exchange Server 2003. For information about how to properly configure a server to run both Windows SharePoint Services and Exchange Server 2003, see Microsoft Knowledge Base article 823265, "You receive a "Page not found" error message when you use Outlook Web Access (OWA) to browse the Exchange Server 2003 client after you install Windows SharePoint Services" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=823265). For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.