Symptoms
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.
Resolution
To fix this issue, install Cumulative Update 13 for Exchange Server 2013 or a later cumulative update for Exchange Server 2013.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.
