We're just beginning our migration of mailboxes from Exchange 2010 to Exchange 2013. Many of our users have additional mailboxes in their Outlook. We've found in our testing that if a mailbox is moved to Exchange 2013 and they need to open an additional mailbox still on Exchange 2010, they receive a proxy certificate error in Outlook. Our testing has found that if we configure Internal Clients to "Connect using SSL only", the connections are seamless.
At first we tried a Group Policy to set "Connect using SSL only" on clients but soon found that Autodiscover reset our policy back to not use SSL. At that point I contacted PSS and opened a ticket.
Microsoft told me that the way to do this was to change the InternallientsRequireSSL to $true. In addition we'll need to change our ClientAuthenticationMethod from Ntlm to Basic. Our tests show that doing that will prompt everyone for credentials when they open Outlook.
Has anyone grappled with this one in a migration before?
Orange County District Attorney