Exchange 2010 mailbox prompts for authentication to Exchange 2013 mailbox

Question

I am in the process of a 2010 to 2013 migration. The only issue I can't seem to manage is an authentication issue with Outlook 2010. My Outlook profile consists of my Exchange 2013 mailbox and a shared mailbox on Exchange 2010. Initially, Outlook was prompting
for authentication to the Exchange 2010 mailbox. Regardless of whether I entered the correct credentials or simply cancelled the prompt, I still had full access to both mailboxes (including Public Folders on 2010). The authentication prompt was removed with
the following command:
Get-OutlookAnywhere -Server my2013exchserver | Set-OutlookAnywhere -InternalClientsRequireSsl $true
The second issue I now have is the reverse of the above: an Exchange 2010 user is prompted for authentication to an Exchange 2013 mailbox. How do I begin to troubleshoot this problem - should I run the same command (above) on 2010? I don't quite understand
how Outlook communicates with Exchange but I am thinking there is an incorrect setting on one of the Virtual Directories(?).
Many thanks.

Answer 1

Hi Dennis,
Please open Outlook - press CTRL key - right click on the Outlook icon from right bottom corner taskbar –Connection Status to check the connection for your Exchange 2010 mailbox with shared 2013 mailbox. The following example in my test results:
Please check your connection authentication. We can  run the following command to set your Outlook Anywhere for Exchange 2013:
Set-OutlookAnywhere -Identity "E15-01\Rpc (Default Web Site)" -InternalClientAuthenticationMethod Ntlm -ExternalClientAuthenticationMethod Basic -ExternalClientsRequireSsl $True -InternalClientsRequireSsl $true
In Outlook side, please ensure the following settings in Account Settings:
In Security tab, make sure Always prompt for logon credentials is unchecked and Logon network security is set to Negotiate Authentication.
Regards,
Winnie Liang
TechNet Community Support