Coexistence between Exchange 2010 and 2013 is fairly new still; so a few bugs is to be expected. This is however a rather large one.
Credential prompts in Outlook (I’ve seen this in both 2010 and 2013) is usually an indicator of authentication/virtual directory configuration errors.
What I’ve seen a few times now is that if you have this scenario:
- User mailbox is on Exchange 2013
- User accesses resoruces (public folders or shared mailbox) on Exchange 2010
- Exchange uses single namespace
You will get a logon prompt in order to access the 2010 resources. And often it won’t even work. The mailbox works if you just cancel the logon prompt; but access to the resources is dead.
This is, as I suspected, a bug in Outlook:
For Outlook 2010, this issue is fixed in the June 11, 2013 hotfix package. For more information about obtaining the hotfix, click the following article number to view the article in the Microsoft Knowledge Base:2817371 Description of the Outlook 2010 hotfix package (Outlook-x-none.msp): June 11, 2013
I’ve yet to try this hotfix, but it will be worth a shot. If anyone gets a chance to try, drop me a line!
A workaround, which I have yet to try, is to abandon single namespace so External and InternalURI are separate. I will test and see how that goes.