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Exchange 2010 mailbox not able to access auto-mapped Exchange 2013 CU3 mailbox

We have coexistence of Exchange 2010 SP3 and Exchange 2013 CU3. Outlook Anywhere and Autodiscover point to Exchange 2013 CAS server and everything works fine irrespective of the mailbox being located on Exchange 2010 or Exchange 2013. But when tried to access auto mapped Exchange 2013 mailbox from primary Exchange 2010 mailbox it errors stating ” Cannot expand the folder. The set of folders cannot be opened. Microsoft Exchange is not available. Either there are network problems or the Exchange server is down for maintenance”.

Exchange 2013 OutlookAnywhere “Externalclientauthenticationmethod” is Basic and “Internalclientauthencitcationmethod” is NTLM. Everything is setup as per the Tech-net recommendations.

Checked both these articles but still it is not working:



Ans: It is an issue with Exchange 2010 Sp3 Rollup 4. Once you upgrade it to Rollup 5 it resolves the issue.

You can download RU5 from the following:


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