I am moving from Exchange 2010 SP3 to Exchange 2013 CU3. All has been going well until OWA. When users hit the URL (internally or externally; same) the blue OWA login screen appears fine. When I logon with an account that's on 2013, it works flawlessly. At first, when I logged on with an account on 2010, an extra /owa got appended to the end of the URL (i.e.,https://server/owa/owa) and I was not connected to the mailbox. I found that I could simply backspace the extra owa out, hit ENTER and be connected to the 2010 mailbox. However, now there is no hand-off to the 2010 CAS/OWA at all.
I guess I just need overall help with getting the virtual directories and authentications set properly. Thank you for any help.