IMAP with NTLM fails if a user's UPN and primary SMTP address don't match in Exchange Server 2013


This issue occurs when your user principal name (UPN) differs from your primary SMTP address in a Microsoft Exchange Server 2013 environment. 

When this issue occurs, Internet Message Access Protocol (IMAP) doesn't work with the Windows Challenge/Response (NTLM) authentication protocol.


To fix this issue, install Cumulative Update 13 for Exchange Server 2013 or a later cumulative update for Exchange Server 2013.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.


Learn about the terminology that Microsoft uses to describe software updates.

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