Just installed Exchange 2013 MBX and CAS on a single machine that I added to an Exchange 2010 organization. Using OWA, the user accounts on the 2013 server can get and send mail, but phones and Outlook do not connect unless I rebuild the Outlook profile. Phones don't connect at all and just ask for a login and don't verify setting up new account settings. I get a 403 error from the options test using ExRCA. Users whose mailboxes are on the 2010 MBX server are unaffected. Any idea what is going on here?