We are currently running Exchange 2007, 2010 and 2013 in the same site. Our external connections point to our production namespace (company.domain.com) which is our 2013 CAS servers. We have a legacy namespace for our 2007 environment. Our 2010 server have no mailboxes and will not be used, it has it's own namespace. We have one mailbox that 5 ad accounts access, They do not have their own mailboxes they all access this one. It always worked withhttps://mail.domain.com/owa/username@domain.com. Since we moved our connections to 2013 they can no longer login to this account. They get the error "Outlook Web Access could not find a mailbox for EXCHANGE\Administrator. If the problem continues, contact technical support for your organization and tell them the following: The mailbox may be stored on a Microsoft Exchange 2000 or Microsoft Exchange 2003 server, or the Active Directory user account was created recently and has not yet replicated to the Active Directory site where this Client Access server is hosted."
Any assistance appreciated.